Health care merger and acquisition activity has increased since enactment of the Affordable Care Act in 2010. Proceeds from transactions involving nonprofit hospitals, health systems, and health plans will endow philanthropic foundations, collectively known as health legacy foundations. Building on work by Grantmakers In Health, we undertook a systematic search for these foundations and generated a newly updated, comprehensive database. We found 306 organizations in forty-three states that have been endowed with proceeds from the sale, merger, lease, joint venture, or other restructuring of nonprofit health care assets. These health legacy foundations had $26.2 billion in assets in 2010. Concentrated in the southern United States, foundations originating from hospitals and specialty care facilities (86.6 percent) held mean assets of $64.7 million per funder and typically restricted grants to local communities. Foundations formed from health plans (13.4 percent) held higher mean assets ($222 million), usually served larger areas, and were more likely to engage in health care advocacy. Recent transactions involving smaller and stand-alone nonprofit hospitals will infuse many more communities with unprecedented charitable wealth.