The last century has seen large changes in land-use and land-cover. We reconstructed the history of conservation land acquisition (where, when, how much and what) from 1850 to 2010 in the San Francisco Bay Area, California, U.S.A. We hypothesized that the process of land acquisition would be characterized by a fill-in effect – as acquisitions are pursued over time, they complement prior acquisitions by adding more area and new or underrepresented land-cover types. We also hypothesized that strategic land acquisition over time would result in representation of all land-cover types, and that these types would subsequently show little transition, except in heavily disturbed locations, such as previously logged redwood forests. Acquisition of conservation lands was continuous and currently represents 31.7% of the Bay Area. Special Districts (local government units delivering a specific service – parks) acquired more area, and cities acquired numerous small properties. There was a fill-in effect with fewer and larger parcels acquired before 1940 while later acquisitions were more numerous but smaller. At least 20% of every land-cover type is currently conserved, showing the historic complementarity of strategic acquisitions. Land-cover change was less than 40% in early acquisitions, between 70 and 80% on degraded lands in mid-century, and 45% in recent acquisitions. The history of conservation land acquisition has led to a representative conservation network in the San Francisco Bay Area. We believe that reconstructing conservation history can unveil past trends, permit assessment of success, and identify challenges to represent biodiversity within a conservation network.