Kassidy is a variant of Cassidy, an Irish surname from Ó Caiside that is usually explained as "curly-haired". Like Cassidy it became a girls' name in the United States in the 1980s and 1990s, and the K spelling followed the fashion of Kaylee and Kennedy. Kassidy peaked at number 314 in 2000, stayed in the top 500 until the mid-2010s and dropped to number 1039 in 2025.