Cohen & Steers reports 14.56M shares (4.89%) of Iron Mountain

Cohen & Steers, Inc. amended a Schedule 13G reporting beneficial ownership of Iron Mountain, Inc. common stock.

Rhea-AI Filing Summary

Cohen & Steers, Inc. amended a Schedule 13G reporting beneficial ownership of Iron Mountain, Inc. common stock. The filing states 14,555,629 shares beneficially owned, representing 4.89% of the class, with 11,657,422 shares of sole voting power and 14,555,629 shares of sole dispositive power. The filing lists related entities and principal addresses and is signed by compliance officers.

Insights

Institutional Ownership Analyst

Large investment manager reports a sub-5% stake in IRM with clear voting and dispositive authority.

The filing shows Cohen & Steers exercises sole voting power over 11,657,422 shares and sole dispositive power over 14,555,629 shares, indicating direct control of voting and sale decisions for these holdings. The percentage shown is 4.89% of the class.

Account-level holdings are held across named affiliates; the filing notes these securities are held for account holders. Subsequent filings would update any ownership threshold changes.

Compliance & Regulatory Advisor

Amendment clarifies entity classification and custodial treatment of holdings.

The amendment lists Cohen & Steers and four affiliated entities with principal addresses and citizenships, and states that certain affiliates hold securities on behalf of account holders. The signature block shows compliance officers certified the amendment.

This is a routine Section 13 filing to report beneficial ownership and related entity structure; no enforcement or corrective language is present.

Key Figures

Beneficially owned: 14,555,629 shares Percent of class: 4.89% Sole voting power: 11,657,422 shares +3 more

6 metrics

Beneficially owned 14,555,629 shares Amount beneficially owned reported on Schedule 13G/A

Percent of class 4.89% Percent of common stock reported

Sole voting power 11,657,422 shares Shares with sole power to vote

Sole dispositive power 14,555,629 shares Shares with sole power to dispose

CUSIP 46284V101 Iron Mountain, Inc. common stock identifier

Filing signature date 05/07/2026 Dates on signature block

Key Terms

Beneficially owned, Sole dispositive power, CUSIP, Schedule 13G/A

4 terms

Beneficially owned regulatory

"Amount beneficially owned: 14,555,629"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

Sole dispositive power regulatory

"Sole power to dispose: 14,555,629"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

CUSIP technical

"CUSIP No.: 46284V101"

A CUSIP is a nine-character alphanumeric code that uniquely identifies a U.S. or Canadian financial security—such as a stock, bond, or fund share—like a Social Security number for an investment. It matters to investors because brokers, exchanges and record-keepers use the CUSIP to match trades, track ownership, settle transactions and pull accurate records, reducing errors and ensuring money and securities go to the right place.

Schedule 13G/A regulatory

"Amendment No. 2 ) Iron Mountain, Inc."

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What stake does Cohen & Steers report in Iron Mountain (IRM)?

Cohen & Steers reports 14,555,629 shares beneficially owned, equal to 4.89% of Iron Mountain's common stock. The filing lists voting and dispositive powers and affiliated entities holding accounts on behalf of clients.

How many shares does Cohen & Steers have voting control over at IRM?

The filing states 11,657,422 shares as the number with sole voting power. It also reports 14,555,629 shares as sole dispositive power, indicating authority to direct sales.

Which Cohen & Steers entities are named in the Schedule 13G/A for IRM?

The filing names Cohen & Steers, Inc.; Cohen & Steers Capital Management, Inc.; Cohen & Steers UK Ltd; Cohen & Steers Asia Ltd; Cohen & Steers Ireland Ltd with their principal addresses and citizenships as provided in the amendment.

Does the filing indicate who ultimately benefits from the IRM shares?

The filing states the affiliates hold securities for the benefit of their respective account holders; beneficiaries have the right to receive dividends or sale proceeds for accounts holding the reported shares.

What date and identifiers are included in the amendment reporting IRM ownership?

The CUSIP listed is 46284V101 and the amendment header shows 04/30/2026; signature dates appear as 05/07/2026 on the executed amendment.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 05/07/2026 - 09:00 AM EDT Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)

Iron Mountain, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

46284V101

(CUSIP Number)

04/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 46284V101

1

Names of Reporting Persons

Cohen & Steers, Inc.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 11,657,422.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 14,555,629.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

14,555,629.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

4.89 %

12

Type of Reporting Person (See Instructions)

HC, CO

SCHEDULE 13G

CUSIP Number(s): 46284V101

1

Names of Reporting Persons

Cohen & Steers Capital Management, Inc.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

NEW YORK

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 11,580,917.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 14,397,690.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

14,397,690.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

4.84 %

12

Type of Reporting Person (See Instructions)

IA, CO

SCHEDULE 13G

CUSIP Number(s): 46284V101

1

Names of Reporting Persons

Cohen & Steers UK Limited

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED KINGDOM

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 60,085.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 141,519.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

141,519.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.05 %

12

Type of Reporting Person (See Instructions)

IA, CO

SCHEDULE 13G

CUSIP Number(s): 46284V101

1

Names of Reporting Persons

Cohen & Steers Asia Limited

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

HONG KONG

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

0.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.00 %

12

Type of Reporting Person (See Instructions)

IA, CO

SCHEDULE 13G

CUSIP Number(s): 46284V101

1

Names of Reporting Persons

Cohen & Steers Ireland Limited

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

IRELAND

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 16,420.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 16,420.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

16,420.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.01 %

12

Type of Reporting Person (See Instructions)

FI, CO

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Iron Mountain, Inc.
(b)	Address of issuer's principal executive offices: 85 New Hampshire Avenue, Suite 150, Portsmouth, NH 03801 USA
Item 2.
(a)	Name of person filing: Cohen & Steers, Inc. Cohen & Steers Capital Management, Inc. Cohen & Steers UK Ltd Cohen & Steers Asia Ltd Cohen & Steers Ireland Ltd
(b)	Address or principal business office or, if none, residence: The principal address for Cohen & Steers, Inc. and Cohen & Steers Capital Management, Inc. is: 1166 Avenue of the Americas, 30th Floor New York, NY 10036 The principal address for Cohen & Steers UK Ltd. is: The Burlian, 2nd Floor 3 Dering Street, London W1S 1AA United Kingdom The principal address for Cohen & Steers Asia Ltd. is: 3301B, 33rd Floor, The Henderson 2 Murray Road Central, Hong Kong The principal address for Cohen & Steers Ireland Ltd. is: Suite G01 81 Merrion Square South Dublin 2 D02 NR12 Ireland
(c)	Citizenship: Cohen & Steers, Inc: Delaware corporation Cohen & Steers Capital Management, Inc: New York corporation Cohen & Steers UK Ltd: United Kingdom Private Limited Company Cohen & Steers Asia Ltd: Asia Private Limited Company Cohen & Steers Ireland Ltd: Ireland Private Limited Company
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 46284V101
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
	Corporation
Item 4.	Ownership
(a)	Amount beneficially owned: 14,555,629
(b)	Percent of class: 4.89%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 11,657,422
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 14,555,629
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Ownership of 5 percent or less of a class
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. Each of Cohen & Steers Capital Management, Inc., Cohen & Steers UK Ltd., Cohen & Steers Asia Ltd. and Cohen & Steers Ireland Ltd. holds the securities of the Issuer to which this statement relates for the benefit of their respective account holders. Such account holders have the right to receive or the power to direct the receipt of dividends from, or proceeds from the sale of, the securities of the Issuer that are held on their behalf.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. Cohen & Steers, Inc. holds a 100% interest in Cohen & Steers Capital Management, Inc., Cohen & Steers UK Ltd., Cohen & Steers Asia Ltd. (investment advisors registered under Section 203 of the Investment Advisers Act) and Cohen & Steers Ireland Ltd. (a non-US institution).
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Cohen & Steers, Inc.

Signature:	/s/ Nargis Hilal
Name/Title:	SVP, Global Chief Compliance Officer & Associate General Counsel
Date:	05/07/2026

Cohen & Steers Capital Management, Inc.

Signature:	/s/ Nargis Hilal
Name/Title:	SVP, Global Chief Compliance Officer & Associate General Counsel
Date:	05/07/2026

Cohen & Steers UK Limited

Signature:	/s/ Nargis Hilal
Name/Title:	SVP, Global Chief Compliance Officer & Associate General Counsel
Date:	05/07/2026

Cohen & Steers Asia Limited

Signature:	/s/ Catherine Cheng
Name/Title:	VP, Compliance Officer
Date:	05/07/2026

Cohen & Steers Ireland Limited

Signature:	/s/ Alan Cooper
Name/Title:	VP, Compliance Officer
Date:	05/07/2026