Tiernan is a distinctive boys' name in United States, ranking #2501 in 1998 with 35 recorded births. The name reached its all-time peak in 2007 with 86 births ranking #1738. Since 1996, the popularity has increased by 105.9%. In 1998, approximately 1 in every 54,609 boys born was named Tiernan. FALLING Recent data shows the name is currently falling.