Iron Mountain Incorporated
MX ˙ BMV ˙ US46284V1017
SecurityMX:IRM1 / Iron Mountain Incorporated
InstitutionDimensional Fund Advisors Lp
Latest Disclosed Ownership4,552,286 shares
Latest Disclosed Value $ 464,930,903
Dimensional Fund Advisors Lp reports 2.78% increase in ownership of IRM1 / Iron Mountain Incorporated

On May 7, 2026 - Dimensional Fund Advisors Lp filed a 13F-HR form disclosing ownership of 4,552,286 shares of Iron Mountain Incorporated (MX:IRM1) valued at $464,930,903 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 12, 2026 disclosing 4,429,359 shares of Iron Mountain Incorporated. This represents a change in shares of 2.78% during the quarter.

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)
2026-05-07 2026-03-31 13F IRON MTN INC DEL COM 46284V101 4,552,286 122,927 2.78 464,931 26.54 0.0966
2026-02-12 2025-12-31 13F IRON MTN INC DEL COM 46284V101 4,429,359 81,320 1.87 367,418 -17.10 0.0771
2025-11-12 2025-09-30 13F IRON MTN INC DEL COM 46284V101 4,348,039 55,273 1.29 443,222 0.66 0.0951
2025-08-12 2025-06-30 13F IRON MTN INC DEL COM 46284V101 4,292,766 36,349 0.85 440,311 20.23 0.1019
2025-05-13 2025-03-31 13F IRON MTN INC DEL COM 46284V101 4,256,417 37,154 0.88 366,210 -17.42 0.0910
2025-02-13 2024-12-31 13F IRON MTN INC DEL COM 46284V101 4,219,263 15,097 0.36 443,476 -11.23 0.1065
2024-11-07 2024-09-30 13F IRON MTN INC DEL COM 46284V101 4,204,166 -81,902 -1.91 499,562 30.05 0.1212
2024-08-09 2024-06-30 13F IRON MTN INC DEL COM 46284V101 4,286,068 -525 -0.01 384,117 11.72 0.1003
2024-05-10 2024-03-31 13F IRON MTN INC DEL COM 46284V101 4,286,593 -1,806 -0.04 343,828 14.57 0.0931
2024-02-07 2023-12-31 13F IRON MTN INC DEL COM 46284V101 4,288,399 -15,517 -0.36 300,106 17.29 0.0876
2023-11-09 2023-09-30 13F IRON MTN INC DEL COM 46284V101 4,303,916 32,452 0.76 255,872 5.43 0.0839
2023-08-09 2023-06-30 13F IRON MTN INC DEL COM 46284V101 4,271,464 52,274 1.24 242,702 8.72 0.0774
2023-05-12 2023-03-31 13F IRON MTN INC DEL COM 46284V101 4,219,190 116,057 2.83 223,231 109,326.96 0.0752
2023-02-09 2022-12-31 13F IRON MTN INC DEL COM 46284V101 4,103,133 54,106 1.34 205 -99.89 0.0604
2022-11-10 2022-09-30 13F IRON MTN INC DEL COM 46284V101 4,049,027 -9,556 -0.24 178,036 -9.90 0.0684
2022-08-12 2022-06-30 13F IRON MTN INC COM 46284V101 4,058,583 -6,850 -0.17 197,605 -12.28 0.0709
2022-05-13 2022-03-31 13F IRON MTN INC COM 46284V101 4,065,433 -84,543 -2.04 225,266 3.73 0.0694
2022-02-09 2021-12-31 13F IRON MTN INC COM 46284V101 4,149,976 -72,078 -1.71 217,169 18.38 0.0657
2021-11-12 2021-09-30 13F IRON MTN INC COM 46284V101 4,222,054 -44,123 -1.03 183,457 1.61 0.0591
2021-08-12 2021-06-30 13F IRON MTN INC COM 46284V101 4,266,177 14,291 0.34 180,545 14.73 0.0572
2021-05-14 2021-03-31 13F IRON MTN INC COM 46284V101 4,251,886 -15,688 -0.37 157,364 25.08 0.0520
2021-03-08 2020-12-31 13F/A-2 IRON MTN INC COM 46284V101 4,267,574 -92,296 -2.12 125,807 7.71 0.0454
2021-02-11 2020-12-31 13F IRON MTN INC COM 46284V101 4,267,574 -92,296 125,807 45,434.8014
2020-11-12 2020-09-30 13F IRON MTN INC COM 46284V101 4,359,870 -41,696 -0.95 116,800 1.67 0.0495
2020-08-13 2020-06-30 13F IRON MTN INC COM 46284V101 4,401,566 16,081 0.37 114,876 10.05 0.0505
2020-05-14 2020-03-31 13F IRON MTN INC COM 46284V101 4,385,485 -31,588 -0.72 104,386 -25.85 0.0544
2020-02-14 2019-12-31 13F IRON MTN INC COM 46284V101 4,417,073 38,156 0.87 140,770 -0.75 0.0513
2019-11-12 2019-09-30 13F IRON MTN INC COM 46284V101 4,378,917 171,346 4.07 141,831 7.70 0.0551
2019-08-13 2019-06-30 13F IRON MTN INC COM 46284V101 4,207,571 40,947 0.98 131,693 -10.87 0.0511
2019-08-12 2019-03-31 13F/A-2 IRON MTN INC COM 46284V101 4,166,624 38,825 0.94 147,751 10.44 0.0588
2019-05-10 2019-03-31 13F IRON MTN INC COM 46284V101 4,166,624 38,825 147,751
2019-02-26 2018-12-31 13F/A-1 IRON MTN INC COM 46284V101 4,127,799 45,950 1.13 133,783 -5.05 0.0606
2019-02-13 2018-12-31 13F IRON MTN INC COM 46284V101 4,127,799 45,950 133,783
2018-11-13 2018-09-30 13F IRON MTN INC COM 46284V101 4,081,849 58,036 1.44 140,901 0.02 0.0536
2018-08-10 2018-06-30 13F IRON MTN INC COM 46284V101 4,023,813 99,620 2.54 140,871 9.25 0.0562
2018-05-11 2018-03-31 13F IRON MTN INC COM 46284V101 3,924,193 173,605 4.63 128,948 -8.88 0.0537
2018-02-12 2017-12-31 13F IRON MTN INC COM 46284V101 3,750,588 139,758 3.87 141,512 0.75 0.0587
2017-11-13 2017-09-30 13F IRON MTN INC COM 46284V101 3,610,830 80,395 2.28 140,460 15.79 0.0614
2017-08-11 2017-06-30 13F IRON MTN INC COM 46284V101 3,530,435 124,704 3.66 121,305 -0.14 0.0560
2017-05-12 2017-03-31 13F IRON MTN INC COM 46284V101 3,405,731 94,324 2.85 121,480 12.95 0.0581
2017-02-09 2016-12-31 13F IRON MTN INC COM 46284V101 3,311,407 275,336 9.07 107,554 -5.61 0.0537
2016-11-10 2016-09-30 13F IRON MTN INC COM 46284V101 3,036,071 404,230 15.36 113,945 8.70 0.0616
2016-08-09 2016-06-30 13F IRON MTN INC COM 46284V101 2,631,841 29,225 1.12 104,825 18.78 0.0603
2016-05-13 2016-03-31 13F IRON MTN INC COM 46284V101 2,602,616 126,417 5.11 88,253 31.95 0.0528
2016-02-10 2015-12-31 13F IRON MTN INC COM 46284V101 2,476,199 670,436 37.13 66,885 19.41 0.0417
2015-11-13 2015-09-30 13F IRON MTN INC COM 46284V101 1,805,763 637,488 54.57 56,013 54.66 0.0368
2015-08-14 2015-06-30 13F IRON MTN INC COM 46284V101 1,168,275 -16,405 -1.38 36,218 -16.20 0.0222
2015-05-14 2015-03-31 13F IRON MTN INC COM 46284V101 1,184,680 379,921 47.21 43,218 38.89 0.0273
2015-02-06 2014-12-31 13F IRON MTN COM 462846106 804,759 125,266 18.44 31,116 40.23 0.0204
2014-11-13 2014-09-30 13F IRON MTN COM 462846106 679,493 -92,526 -11.98 22,190 -18.91 0.0157
2014-08-08 2014-06-30 13F IRON MTN COM 462846106 772,019 244,877 46.45 27,366 88.33 0.0190
2014-05-14 2014-03-31 13F IRON MTN COM 462846106 527,142 190,494 56.59 14,531 42.21 0.0109
2014-02-12 2013-12-31 13F IRON MTN COM 462846106 336,648 5,715 1.73 10,218 14.24 0.0080
2013-11-13 2013-09-30 13F IRON MTN COM 462846106 330,933 7,000 2.16 8,944 3.75 0.0077
2013-08-15 2013-06-30 13F IRON MTN COM 462846106 323,933 323,933 8,621 0.0081
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.