Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U.S. state of Tennessee, about 25 miles (40 km) west of Knoxville. Oak Ridge's population was 27,387 at the 2000 census. The portion of the city located in Anderson County is included in the Knoxville Metropolitan Area, while the portion located in Roane County is included in the Harriman, Tennessee Micropolitan Statistical Area; both of these areas are components of the Knoxville-Sevierville-La Follette, TN Combined Statistical Area. Oak Ridge's nicknames are the Atomic City, the Secret City, the Ridge and the City Behind the Fence. Oak Ridge was established in the early 1940s as a base for the Manhattan Project—the massive U.S. government operation that developed the atomic bomb. Scientific development still plays a crucial role in the city's economy and culture in general.