In 1913, the Illinois Legislature enacted the Forest Preserve District Act. After adoption of the Act by voters in Cook County, the Chicago metropolitan area became among the first in the USA to establish a park system with an outer ring of nature preserves. This article chronicles the story of how the Cook County Forest Preserve District was established, its historical context and its influence on planning practice. It contends that although Chicago was not the originator of the idea of outer parks, it added significantly to development of the concept of comprehensive park system planning. The article contends that the paradigm of park management changed from conservation of the native landscape to multiple use management during the 20-year struggle to establish the district, and that passage of the Act was largely the result of the efforts of two individuals - Dwight Perkins and Jens Jensen.