As an English name it has been in use since the Middle Ages, originally in the form Clare, though the Latinate spelling Clara overtook it in the 19th century and became very popular. It declined through most of the 20th century (being eclipsed by the French form Claire in English-speaking countries), though it has since recovered somewhat.
This name was borne by the heroine of Lewis Carroll's novels Alice's Adventures in Wonderland (1865) and Through the Looking Glass (1871).
In Britain the parallel form Alice, derived via Old French, has historically been more common than Adelaide, though this form did gain some currency in the 19th century due to the popularity of the German-born wife of King William IV, for whom the city of Adelaide in Australia was named in 1836.