Okayama (ōkäˈyämä) [key], city (1990 pop. 593,730), capital of Okayama prefecture, SW Honshu, Japan, on an inlet of the Inland Sea. It is a railroad hub and industrial and marketing center. Machinery, cotton textiles, chemicals, and rubber goods are produced in Okayama. The city has a 16th-century feudal castle, an 18th-century park, and Okayama Univ., which has a famous medical college. Okayama prefecture (1990 pop. 1,925,913), 2,721 sq mi (7,047 sq km), which relies mainly on agriculture, has an oil refinery and automobile, petrochemical, and steel industries.