Cassidy is a moderately popular girls' name in United States, ranking #244 in 2009 with 1,359 recorded births. The name reached its all-time peak in 1999 with 3,395 births ranking #99. Since 1996, the popularity has decreased by 52.2%. In 2009, approximately 1 in every 1,352 girls born was named Cassidy. STABLE Recent data shows the name is currently stable.