Cassidy is a popular girls' name in United States, ranking #99 in 1999 with 3,395 recorded births. The name reached its all-time peak in 1999 with 3,395 births ranking #99. Since 1996, the popularity has increased by 19.4%. In 1999, approximately 1 in every 522 girls born was named Cassidy. STABLE Recent data shows the name is currently stable.