Tsukuba (つくば市 Tsukuba-shi?) is a city located in Ibaraki Prefecture, in the northern Kantō region of Japan. As of September 2015, the city had an estimated population of 223,151 and a population density of 787 persons per km². Its total area is 283.72 km2 (109.54 sq mi). It is known as the location of the Tsukuba Science City (筑波研究学園都市 Tsukuba Kenkyū Gakuen Toshi?), a planned science park developed in the 1960s.