Tiernan is a distinctive boys' name in United States, ranking #2339 in 1999 with 39 recorded births. The name reached its all-time peak in 2007 with 86 births ranking #1738. Since 1996, the popularity has increased by 129.4%. In 1999, approximately 1 in every 49,233 boys born was named Tiernan. FALLING Recent data shows the name is currently falling.