Who owns Iron Mountain (IRM)?
136 holders named in SEC filings declare between 58.8% and 80.9% of Iron Mountain's shares outstanding, as of Sep 1, 2026. The largest are Vanguard (16.0%), BlackRock (11.3%) and State Street (5.9%); the five largest hold 40.2% together. Another 1,032 institutions hold small positions worth 6.1%. At least 13.0% of the shares appear in no ownership filing: investors who do not have to report, mostly individuals. From Mar 31, 2026 to Jun 30, 2026, institutions that filed both quarters bought 4.8% and sold 5.0% of the shares, a net sale of 0.17%; 134 opened a position, 433 added, 378 reduced and 58 sold out. Biggest buyers: UBS (+3.3M shares) and Vanguard (+816,098 shares). Biggest sellers: Cohen & Steers, Inc. (-4.1M) and Daiwa Securities Group Inc. (-1.2M). Schedule 13D/G filings since Mar 31, 2026: Cohen & Steers, Inc. fell below 5% (4.9% still declared) on Apr 30, 2026. Directors and officers, from their latest Form 4: Kent P. Dauten (0.41%). Over time, 1,160 managers declared Iron Mountain in their 13F for Q2 2026, against 541 for Q4 2019: together at most 86.4% of the shares outstanding, against 83.4%.
| Holder | Filing | Share of capital | As of | Holding since (13F) |
|---|---|---|---|---|
| Vanguard | 13F | 16.0% | Jun 30, 2026 | Q4 2019 or earlier |
| BlackRock | 13F | 11.3% | Jun 30, 2026 | Q4 2019 or earlier |
| State Street | 13F | 5.9% | Jun 30, 2026 | Q4 2019 or earlier |
| Cohen & Steers, Inc. | 13F | 4.0% | Jun 30, 2026 | Q4 2021 |
| Geode Capital | 13F | 2.9% | Jun 30, 2026 | Q4 2019 or earlier |
| Fidelity (FMR) | 13F | 2.6% | Jun 30, 2026 | Q4 2019 or earlier |
| Dimensional | 13F | 1.6% | Jun 30, 2026 | Q4 2019 or earlier |
| Morgan Stanley | 13F | 1.5% | Jun 30, 2026 | Q4 2019 or earlier |
| PRINCIPAL FINANCIAL GROUP INC | 13F | 1.5% | Jun 30, 2026 | Q4 2019 or earlier |
| Charles Schwab | 13F | 1.4% | Jun 30, 2026 | Q4 2019 or earlier |
| Northern Trust | 13F | 1.4% | Jun 30, 2026 | Q4 2019 or earlier |
| Norges Bank | 13F | 1.4% | Jun 30, 2026 | Q4 2019 or earlier |
| UBS | 13F | 1.4% | Jun 30, 2026 | Q4 2019 or earlier |
| Invesco | 13F | 1.4% | Jun 30, 2026 | Q4 2019 or earlier |
| Legal & General | 13F | 1.1% | Jun 30, 2026 | Q4 2019 or earlier |
| Deutsche Bank | 13F | 1.0% | Jun 30, 2026 | Q4 2019 or earlier |
| Goldman Sachs | 13F | 0.95% | Jun 30, 2026 | Q4 2019 or earlier |
| CENTERSQUARE INVESTMENT MANAGEMENT LLC | 13F | 0.78% | Jun 30, 2026 | Q1 2023 |
| Nuveen | 13F | 0.75% | Jun 30, 2026 | Q4 2019 or earlier |
| JPMorgan | 13F | 0.74% | Jun 30, 2026 | Q4 2019 or earlier |
| AQR | 13F | 0.71% | Jun 30, 2026 | Q4 2019 or earlier |
| PRUDENTIAL FINANCIAL INC | 13F | 0.66% | Jun 30, 2026 | Q4 2019 or earlier |
| Vontobel Holding Ltd. | 13F | 0.64% | Jun 30, 2026 | Q3 2025 |
| Daiwa Securities Group Inc. | 13F | 0.63% | Jun 30, 2026 | Q4 2019 or earlier |
| Ameriprise Financial, Inc. | 13F | 0.56% | Jun 30, 2026 | Q4 2019 or earlier |
Iron Mountain institutional ownership over time
| Quarter | 13F managers | Share of the company (upper bound) | Value declared | Held by stock pickers |
|---|---|---|---|---|
| Q4 2019 | 541 | 83.4% | $7.7B | 48.7% |
| Q4 2020 | 580 | 79.8% | $6.8B | 48.7% |
| Q4 2021 | 727 | 78.1% | $11.8B | 45.7% |
| Q4 2022 | 767 | 78.1% | $11.3B | 45.7% |
| Q4 2023 | 880 | 79.9% | $16.3B | 47.7% |
| Q4 2024 | 1,058 | 80.8% | $24.9B | 42.9% |
| Q4 2025 | 1,002 | 87.1% | $21.4B | 45.7% |
| Q2 2026 | 1,160 | 86.4% | $32.4B | 42.8% |
From SEC Form 13F, every quarter since the end of 2019, read like the current quarter: entities of a house summed, a value contradicting its share count set aside. The share of the company is an upper bound — two managers can declare the same shares — over the shares outstanding at that date.