Ibarakiken (prefecture), east-central Honshu, Japan, facing the Pacific Ocean. It is located in the northeastern Kantō Plain. Ibaraki is bordered (south) by the Tone River and contains part of Suigo-Tsukuba Quasi-national Park. Main features of this section of the park include Lake Kasumi (Kasumiga-ura), the second largest Japanese lake after Lake Biwa; the canals and creeks of the Tone River delta; the ancient Shintō Kashima Shrine; and the tourist centre of Itako town.

Ibaraki is basically agricultural, producing cereals, potatoes, and tobacco. Industry increased in the prefecture during the 1960ssecond half of the 20th century, while production in the Tokyo-Yokohama Metropolitan Area declined. There are petrochemical works at Kashima and Kasumi, and electric machinery is built at Hitachinaka. The first Nuclear Energy Research Institute was founded in Tōkaimura in 1956, and Tsukuba Science City was developed in the 1970s and ’80s as Japan’s premier research centre. Many of the cities were castle towns. Mito, the prefectural capital, was developed under the Mito branch of the Tokugawa shogunate; its Kairaku Garden is one of the most celebrated in Japan.

On March 11, 2011, the prefecture was struck by a severe earthquake (magnitude 9.0) centred off northeastern Honshu in the Pacific Ocean. The temblor and subsequent aftershocks caused damage in several localities, but the resultant tsunami, generated by the main quake, inundated and devastated coastal areas. Particularly hard-hit were Hitachinaka and Kitaibaraki. Area 2,354 square miles (6,096 square km). Pop. (20052010 prelim.) 2,975968,167865.