Brennan is a distinctive girls' name in United States, ranking #3782 in 2015 with 40 recorded births. The name reached its all-time peak in 2007 with 100 births ranking #2039. Since 1996, the popularity has decreased by 33.3%. In 2015, approximately 1 in every 44,616 girls born was named Brennan. FALLING Recent data shows the name is currently falling.