Brennan is a moderately popular boys' name in United States, ranking #444 in 2015 with 690 recorded births. The name reached its all-time peak in 2009 with 1,464 births ranking #242. Since 1996, the popularity has decreased by 22.9%. In 2015, approximately 1 in every 2,777 boys born was named Brennan. STABLE Recent data shows the name is currently stable.