Brennan is a distinctive girls' name in United States, ranking #2648 in 2002 with 58 recorded births. This places Brennan in the top 15% of ranked US girls' names for the year. Its actual usage is classified as Rare. The name reached its all-time peak in 2007 with 100 births ranking #2039. In 2002, approximately 1 in every 30,980 girls born was named Brennan. FALLING Recent data shows the name is currently falling.