# Day & Zimmermann Day & Zimmermann is a Single Family Office based in Philadelphia, United States. ## Overview - **Organization type:** Single Family Office - **Headquarters:** Philadelphia, United States - **Region:** North America - **Address:** Philadelphia, PA, United States - **Founded:** 1901 - **Assets under management:** Undisclosed - **Website:** dayzim.com ## Regulatory record - **Reports private funds:** No ## About Day & Zimmermann specializes in construction & engineering, O&M, staffing, security and defense for leading corporations and governments around the world. ## Sectors - Infrastructure - Energy Transition & Renewables - Industrial Tech - Real Estate - Cybersecurity ## People - Harold L. Yoh, III — Chairman and CEO ## Questions ### Who controls Day & Zimmermann and how is the family involved? The Yoh family has controlled Day & Zimmermann since H.L. Yoh joined the firm in 1936. Harold L. Yoh III currently serves as Chairman and CEO. Several other family members hold leadership roles, including Mike Yoh and Daniel Ross. The firm is treated as a family-held industrial enterprise — there is no outside LP base or separated investment portfolio. ### How does Day & Zimmermann generate returns for the family? Rather than earning management fees on outside capital, Day & Zimmermann generates returns through the operating profits of its four divisions: Maintenance & Construction, Munitions, Government Services, and Workforce Solutions. It is an operating company, not an investment manager. Family wealth is tied directly to the firm's success as a government and industrial contractor. ### Does Day & Zimmermann operate as a typical family office that allocates to external funds? No. Day & Zimmermann does not disclose a liquid investment portfolio, fund-of-funds activity, or external capital-allocation function. Its structure more closely resembles a privately held industrial conglomerate than a single-family office — profits are retained and reinvested inside the operating company rather than deployed into third-party assets. ### Which US government agencies are Day & Zimmermann's main clients? The firm's Munitions division manufactures, stores, and demilitarizes ammunition products primarily for the US Department of Defense and approved foreign governments. The Government Services segment provides integrated security, architecture and engineering, and intelligence support to US embassies, law enforcement, and the Navy and Marine Corps. ### How is the philanthropic activity structured? Day & Zimmermann channels its charitable giving through the D&Z Gives Back program, which is part of the operating company. The firm does not appear to maintain a structurally separate family foundation, keeping its community investments integrated with the corporate entity. ### What is the Mason & Hanger relationship to Day & Zimmermann? Mason & Hanger is listed as 'A Day & Zimmermann Company' and functions as the firm's architecture and engineering subsidiary for US government and commercial clients. It has designed a 426-acre law enforcement training campus and provided A&E services for secure diplomatic facilities abroad. ### Does Day & Zimmermann have a venture capital or growth equity arm? There is no disclosed venture capital, growth equity, or independent financial-investment vehicle. The closest parallel is the Yoh.com Workforce Solutions segment, which places technical talent, but this is an operating staffing business, not a principal-investing function. ## Related profiles - [Henry Schein](https://altss.com/profile/henry-schein) - [Compost360](https://altss.com/profile/compost360) --- Last updated: 2026-06-03T20:00:00.000Z Canonical page: https://altss.com/profile/day-and-zimmermann Maintained by Altss — https://altss.com — methodology: https://altss.com/methodology