Dillon is an Irish surname, probably from the Norman de Leon, "of Lyon", though in the United States it is used mostly as a spelling of the Welsh Dylan, which is usually explained as "son of the sea". The spelling peaked with the character Dylan McKay of Beverly Hills, 90210 in the 1990s, when both versions were everywhere. Dillon ranked number 169 in 2000 and has declined steadily since, to number 448 in 2015 and number 930 in 2025.