Tachikawa (立川市, Tachikawa-shi) is a city located in western Tokyo Metropolis, Japan. The city was founded on December 1, 1940. As of February 1, 2010, the city has an estimated population of 178,064 and a population density of 7,303.69 persons per km². The total area is 24.38 km². Showa Memorial Park, an expansive leisure and recreational facility operated by the national government, occupies 1.49 square kilometres of land that was formerly part of Tachikawa Air Base in Tachikawa and neighboring Akishima.