Tiernan is a distinctive boys' name in United States, ranking #1904 in 2003 with 62 recorded births. The name reached its all-time peak in 2007 with 86 births ranking #1738. Since 1996, the popularity has increased by 264.7%. In 2003, approximately 1 in every 31,859 boys born was named Tiernan. FALLING Recent data shows the name is currently falling.