Iron Mountain Incorporated
US ˙ NYSE ˙ US46284V1017

SecurityIRM / Iron Mountain Incorporated
InstitutionNorthern Trust Corp
Latest Disclosed Ownership4,150,486 shares
Latest Disclosed Value $ 423,930,638
Northern Trust Corp reports 0.05% decrease in ownership of IRM / Iron Mountain Incorporated

On May 14, 2026 - Northern Trust Corp filed a 13F-HR form disclosing ownership of 4,150,486 shares of Iron Mountain Incorporated (US:IRM) valued at $423,930,640 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 4,152,569 shares of Iron Mountain Incorporated. This represents a change in shares of -0.05% during the quarter. The current value of the position is $531,054,684 USD.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date		 Effective
Date		Form Security Class ID Avg Price
Paid (Est)		 Reported
Shares		 ΔShares ΔShares
(%)		 Reported
Value
(x1000)		 ΔValue
(%)		 Alloc
(%)		 ΔAlloc ΔAlloc (%) Cost Basis
(x1000)		 Unrealized
Gain/Loss
(x1000)
2026-05-14 2026-03-31 13F IRON MTN INC DEL COM 46284V101 4,150,486 -2,083 -0.05 423,931 23.07 0.0560
2026-02-17 2025-12-31 13F IRON MTN INC DEL COM 46284V101 4,152,569 121,003 3.00 344,456 -16.19 0.0439
2025-11-14 2025-09-30 13F IRON MTN INC DEL COM 46284V101 4,031,566 -36,242 -0.89 410,978 -1.50 0.0526
2025-08-13 2025-06-30 13F IRON MTN INC DEL COM 46284V101 4,067,808 -199,516 -4.68 417,235 13.64 0.0574
2025-05-13 2025-03-31 13F IRON MTN INC DEL COM 46284V101 4,267,324 -59,152 -1.37 367,161 -19.26 0.0545
2025-02-14 2024-12-31 13F IRON MTN INC DEL COM 46284V101 4,326,476 1,554,746 56.09 454,756 38.07 0.0644
2024-11-13 2024-09-30 13F IRON MTN INC DEL COM 46284V101 2,771,730 -196,692 -6.63 329,365 23.81 0.0539
2024-08-14 2024-06-30 13F IRON MTN INC DEL COM 46284V101 2,968,422 52,798 1.81 266,030 13.75 0.0448
2024-05-14 2024-03-31 13F IRON MTN INC DEL COM 46284V101 2,915,624 -214,681 -6.86 233,862 6.76 0.0404
2024-02-13 2023-12-31 13F IRON MTN INC DEL COM 46284V101 3,130,305 -783,523 -20.02 219,059 -5.85 0.0397
2023-11-13 2023-09-30 13F IRON MTN INC DEL COM 46284V101 3,913,828 47,902 1.24 232,677 5.93 0.0451
2023-08-11 2023-06-30 13F IRON MTN INC DEL COM 46284V101 3,865,926 71,749 1.89 219,662 9.42 0.0422
2023-05-15 2023-03-31 13F IRON MTN INC DEL COM 46284V101 3,794,177 57,881 1.55 200,750 7.78 0.0398
2023-02-13 2022-12-31 13F IRON MTN INC DEL COM 46284V101 3,736,296 541,022 16.93 186,254 32.57 0.0391
2022-11-14 2022-09-30 13F IRON MTN INC DEL COM 46284V101 3,195,274 -148,285 -4.43 140,496 -13.70 0.0321
2022-08-12 2022-06-30 13F IRON MTN INC COM 46284V101 3,343,559 -844,101 -20.16 162,798 -29.84 0.0349
2022-05-13 2022-03-31 13F IRON MTN INC COM 46284V101 4,187,660 -371,505 -8.15 232,038 -2.74 0.0408
2022-02-08 2021-12-31 13F IRON MTN INC COM 46284V101 4,559,165 300,897 7.07 238,581 28.95 0.0391
2021-11-15 2021-09-30 13F IRON MTN INC COM 46284V101 4,258,268 594,092 16.21 185,021 19.32 0.0327
2021-08-13 2021-06-30 13F IRON MTN INC COM 46284V101 3,664,176 -57,883 -1.56 155,067 12.57 0.0273
2021-05-12 2021-03-31 13F IRON MTN INC COM 46284V101 3,722,059 109,076 3.02 137,754 29.33 0.0256
2021-02-11 2020-12-31 13F IRON MTN INC COM 46284V101 3,612,983 -69,127 -1.88 106,510 7.97 0.0207
2020-11-16 2020-09-30 13F IRON MTN INC COM 46284V101 3,682,110 -66,108 -1.76 98,644 0.83 0.0216
2020-08-14 2020-06-30 13F IRON MTN INC COM 46284V101 3,748,218 -57,876 -1.52 97,829 8.00 0.0232
2020-05-14 2020-03-31 13F IRON MTN INC COM 46284V101 3,806,094 67,134 1.80 90,584 -23.98 0.0260
2020-02-14 2019-12-31 13F IRON MTN INC COM 46284V101 3,738,960 33,453 0.90 119,160 -0.72 0.0267
2019-11-13 2019-09-30 13F IRON MTN INC COM 46284V101 3,705,507 676 0.02 120,022 3.50 0.0287
2019-08-13 2019-06-30 13F IRON MTN INC COM 46284V101 3,704,831 287,797 8.42 115,962 -4.30 0.0275
2019-05-13 2019-03-31 13F IRON MTN INC COM 46284V101 3,417,034 33,106 0.98 121,169 10.48 0.0299
2019-02-12 2018-12-31 13F IRON MTN INC COM 46284V101 3,383,928 18,543 0.55 109,673 -5.59 0.0308
2018-11-14 2018-09-30 13F IRON MTN INC COM 46284V101 3,365,385 319,235 10.48 116,172 8.93 0.0284
2018-09-18 2018-06-30 13F/A-1 IRON MTN INC COM 46284V101 3,046,150 -109,426 -3.47 106,646 2.85 0.0271
2018-08-14 2018-06-30 13F IRON MTN INC COM 46284V101 3,064,578 -90,998 107,291
2018-05-09 2018-03-31 13F IRON MTN INC COM 46284V101 3,155,576 -62,883 -1.95 103,692 -14.61 0.0270
2018-02-14 2017-12-31 13F IRON MTN INC COM 46284V101 3,218,459 157,550 5.15 121,433 1.98 0.0308
2017-11-13 2017-09-30 13F IRON MTN INC COM 46284V101 3,060,909 327,880 12.00 119,071 26.80 0.0310
2017-08-11 2017-06-30 13F IRON MTN INC COM 46284V101 2,733,029 34,350 1.27 93,906 -2.45 0.0263
2017-05-12 2017-03-31 13F IRON MTN INC COM 46284V101 2,698,679 177,584 7.04 96,261 17.56 0.0278
2017-02-13 2016-12-31 13F IRON MTN INC COM 46284V101 2,521,095 -124,525 -4.71 81,884 -17.53 0.0251
2016-11-09 2016-09-30 13F IRON MTN INC COM 46284V101 2,645,620 -63,323 -2.34 99,290 -7.98 0.0309
2016-08-12 2016-06-30 13F IRON MTN INC COM 46284V101 2,708,943 540,663 24.94 107,896 46.74 0.0350
2016-08-19 2016-03-31 13F/A-1 IRON MTN INC COM 46284V101 2,168,280 11,970 0.56 73,527 26.25 0.0244
2016-05-13 2016-03-31 13F IRON MTN INC COM 46284V101 2,168,280 73,527
2016-02-12 2015-12-31 13F IRON MTN INC COM 46284V101 2,156,310 -246,457 -10.26 58,241 -21.86 0.0193
2015-11-12 2015-09-30 13F IRON MTN INC COM 46284V101 2,402,767 2,402,767 0.00 74,535 0.0249
2015-08-13 2015-06-30 13F IRON MTN INC COM 46284V101 0 -2,865,688 -100.00 0 -100.00
2015-05-14 2015-03-31 13F IRON MTN INC COM 46284V101 2,865,688 665,913 30.27 104,540 22.93 0.0314
2015-02-12 2014-12-31 13F IRON MTN COM 462846106 2,199,775 -522,732 -19.20 85,043 -4.33 0.0257
2014-11-13 2014-09-30 13F Iron Mtn Inc Del COMM 462846106 2,722,507 327,459 13.67 88,890 4.69 0.0279
2014-08-14 2014-06-30 13F IRON MTN COM 462846106 2,395,048 63,253 2.71 84,905 32.07 0.0265
2014-05-14 2014-03-31 13F IRON MTN COM 462846106 2,331,795 -110,844 -4.54 64,287 -13.28 0.0202
2014-02-21 2013-12-31 13F/A-1 IRON MTN COM 462846106 2,442,639 207,622 9.29 74,134 22.76 0.0238
2014-02-12 2013-12-31 13F IRON MTN COM 462846106 2,442,639 74,134
2013-11-13 2013-09-30 13F IRON MTN COM 462846106 2,235,017 72,121 3.33 60,390 4.93 0.0213
2013-08-09 2013-06-30 13F IRON MTN COM 462846106 2,162,896 2,162,896 57,554 0.0209
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.