Irish, English and Scottish, probably derived from Kay, a pet name for any female name beginning with the letter K-, but possibly from Kylie [q.v.].

The derivation is not certain but Kayley is known to have been in use in Scotland long before the upsurge in modern use of Kylie on its resurgence from Australia.

A correspondent in Scotland [AB] has noted that there are many spelling variations, including Kay-lee and Ceilidh. Soundex may help to find these in indexed records.