Fort Riley is a United States Army installation located in North Central Kansas, on the Kansas River, also known as the Kaw, between Junction City and Manhattan. The Fort Riley Military Reservation covers 101,733 acres in Geary and Riley counties. The portion of the fort that contains housing development is part of the Fort Riley census-designated place, with a residential population of 7,761 as of the 2010 census. The fort has a daytime population of nearly 25,000. The ZIP code is 66442.