Tiernan has been given to about 1,676 people in the United States since 1880. It was most common in 2009, which makes it a millennial-parent name.
Its best year was 2009, when 95 babies were given the name, ranking 1787th. The typical living American called Tiernan is about 18 years old today.
Source: US Social Security Administration, national and state name files, 2025 release, and the Office for National Statistics for England and Wales. Etymology researched and written by our editors. Living-population and median-age figures are our own estimates, described in the methodology.