Slough (/ˈslaʊ/) is a town in Berkshire, England, about 20 miles (30 kilometres) west of central London. It is bisected by the A4 and the Great Western Main Line. In 2011, the population of Slough was 140,200 and the most ethnically diverse outside London in the United Kingdom with the highest proportion of religious adherents in England. Before 1974, Slough was in Buckinghamshire.