town and unitary authority in the northeastern part of the geographic and historic county of Wiltshire, southern England. Mostly in a fertile clay valley, the unitary authority is bounded on the north by the upper reaches of the River Thames and on the south by the steep chalk escarpment of the Marlborough Downs. Until 1841 Swindon was a small market town, but, when the Great Western Railway built its main engineering works there, the population rapidly increased to 45,000. During the 1950s the town decided to accept overspill population and industry from Greater London, about 75 miles (120 km) to the east. Considerable redevelopment and rapid growth ensued. However, the railway works closed in the mid-1980s. Insurance and automotive manufacturing are now the town's main industries. The hamlet of Inglesham, northeast of Swindon, has an unrestored, mostly 13th-century church. Area unitary authority, 89 square miles (230 square km). Pop. (2001) town, 155,432; (2005 est.) unitary authority, 184,000.