Views that protected area (PA) expansion relies predominantly on land purchased by government are increasingly being challenged. The inclusion of privately owned PAs (PPAs) in national conservation strategies is now commonplace, but little is known about their long-term persistence and how it compares to that of state-owned PAs. We undertook the first long-term assessment of the dynamics of a national system of terrestrial PPAs, assessing its growth, as well as its resilience to downgrading, downsizing, and degazettement (PADDD). Between 1926 and 2018, 6.2% of all private nature reserves established in South Africa were degazetted, compared to 2.2% of state-owned nature reserves. Privately owned PA growth exceeded that of state-owned PAs. Trends in PA establishment differed between privately owned and state-owned PAs, reflecting different legislative, political, and economic events. Our findings highlight the value of enabling legislative environments to facilitate PPA establishment, and demonstrate the potential of PPAs as a long-term conservation strategy.