Tiernan is a distinctive boys' name in England & Wales, ranking #983 in 2001 with 16 recorded births. The name reached its all-time peak in 1999 with 24 births ranking #697. Since 1996, the popularity has increased by 60.0%. In 2001, approximately 1 in every 17,989 boys born was named Tiernan. FALLING Recent data shows the name is currently falling.