Post–World War II population growth outside Washington, D.C., brought the Potomac River’s watershed under metropolitan oversight. This article examines the history of Loudoun County, Virginia, an agricultural area thirty miles upstream from the District of Columbia, as it faced six proposed urban infrastructure projects between the 1940s and late 1970s. Tracing the history of these proposals reveals the complex interplay between the federal government and its agencies, urban interest groups, local governments, and grassroots environmentalists as each shaped this hinterland’s integration into the Washington metropolis. By underscoring the persistent conflicts between environmental activism, rural boosterism, and metropolitan development within one particular region, this article argues that this process of urban and suburban expansion was often fragmentary, and ultimately dependent as much on national political trends as it was on fragmented regional power structures.