Named after Clapham, whose name may mean the homestead near a hill.
The Domesday Book of 1086 records Clapham as Clopeham, held by Geoffrey de Mandeville; the earliest form, Cloppaham, dates from around 880. The name may also recall a landowner called something like Cloppa. The station opened in 1900 as Clapham Road and was renamed Clapham North on 13 September 1926, when the line was extended to Morden.