Sec Form 4 Filing - Samuels Theodore R. II @ IRON MOUNTAIN INC - 2023-10-13

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Samuels Theodore R. II 2. Issuer Name and Ticker or Trading Symbol IRON MOUNTAIN INC [ IRM] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O IRON MOUNTAIN INCORPORATED, 85 NEW HAMPSHIRE AVENUE, SUITE 150 3. Date of Earliest Transaction (MM/DD/YY) 10/13/2023 (Street) PORTSMOUTH, NH03801 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Phantom Stock ( 1 ) 10/13/2023 A 456.594 ( 2 ) ( 1 ) ( 1 ) Common Stock 456.594 $ 60.23 ( 3 ) 482.062 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Samuels Theodore R. II C/O IRON MOUNTAIN INCORPORATED 85 NEW HAMPSHIRE AVENUE, SUITE 150 PORTSMOUTH, NH03801 X Signatures /s/ Keely Stewart, under Power of Attorney dated July 6, 2023 from Theodore R Samuels 10/17/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Pursuant to the Reporting Person's election to participate in the Iron Mountain Incorporated Directors Deferred Compensation Plan, the shares of phantom stock (the "Phantom Shares") will become payable in shares of Iron Mountain Incorporated common stock ("Common Stock") following the Reporting Person's disability or cessation of service as a director. Each Phantom Share is the economic equivalent of one share of Common Stock. ( 2 )These shares give effect to the Reporting Person's quarterly cash compensation for services on the Iron Mountain Incorporated board of directors as if reinvested in Phantom Shares. ( 3 )The price reported in Column 8 is a weighted average price. These shares of Iron Mountain Incorporated Common Stock were sold in multiple transactions at prices ranging from $60.159 to $60.289, inclusive. The Reporting Person undertakes to provide Iron Mountain Incorporated (the "Company"), any security holder of the Company, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the ranges set forth in this footnote (3).

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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