town and unitary authority, geographic county of Berkshire, England. Most of the unitary authority lies within the historic county of Buckinghamshire, but it also includes Poyle, part of the historic county of Middlesex. It lies on the western periphery of the Greater London metropolitan area, along the Great West Road and M4 motorway. The town of Slough developed into a centre of varied light industries after World War I and has subsequently grown rapidly. Area, unitary authority, 13 square miles (33 square km). Pop. (2005 est.) unitary authority, 117,500; (2001) Slough Urban Area, 141,848.