Brennan is a moderately popular boys' name in United States, ranking #300 in 2004 with 1,061 recorded births. The name reached its all-time peak in 2009 with 1,464 births ranking #242. Since 1996, the popularity has increased by 18.5%. In 2004, approximately 1 in every 1,871 boys born was named Brennan. STABLE Recent data shows the name is currently stable.