Kaycee is a phonetic spelling of the initials K. C. and of Casey, an Irish surname from Ó Cathasaigh that is usually explained as "vigilant" or "watchful". The spelled-out form took hold in the 1980s and 1990s, when Casey was a top 100 name for both sexes. Kaycee peaked at number 1008 in 2000, just outside the top 1000, and has held between number 1200 and 1450 ever since, ranking number 1303 in 2025.