Brennan is a moderately popular boys' name in United States, ranking #274 in 1998 with 1,051 recorded births. The name reached its all-time peak in 2009 with 1,464 births ranking #242. Since 1996, the popularity has increased by 17.4%. In 1998, approximately 1 in every 1,819 boys born was named Brennan. STABLE Recent data shows the name is currently stable.