Tiernan is a distinctive girls' name in United States, ranking #18879 in 2015 with 5 recorded births. This places Tiernan in the bottom 1% of ranked US girls' names for the year. Its actual usage is classified as Rare. The name reached its all-time peak in 2002 with 19 births ranking #6114. In 2015, approximately 1 in every 356,931 girls born was named Tiernan. STABLE Recent data shows the name is currently stable.