Tiernan is a distinctive boys' name in United States, ranking #2145 in 2001 with 49 recorded births. The name reached its all-time peak in 2007 with 86 births ranking #1738. Since 1996, the popularity has increased by 188.2%. In 2001, approximately 1 in every 39,650 boys born was named Tiernan. FALLING Recent data shows the name is currently falling.