Kacey is a spelling of Casey, which comes from the Irish surname O Cathasaigh, "vigilant" or "watchful", and is sometimes used for girls whose initials are K.C. Country singer Kacey Musgraves is the name's most prominent American bearer. Kacey ranked number 845 in the United States in 2000, its best year in this century, and has stayed just outside the top 1000 since, at number 1118 in 2025.