Brennan is a distinctive girls' name in United States, ranking #3271 in 2005 with 47 recorded births. The name reached its all-time peak in 2007 with 100 births ranking #2039. Since 1996, the popularity has decreased by 21.7%. In 2005, approximately 1 in every 39,313 girls born was named Brennan. FALLING Recent data shows the name is currently falling.