Cillian has been given to about 4,090 people in the United States since 1880. It was most common in 2024, which makes it a current name.
Cillian ranks 507th among American boys in 2025, with 595 born that year. Its best year was 2024, when 674 babies were given the name, ranking 463rd. The typical living American called Cillian is about 4 years old today. It is relatively most common in Alaska, where it accounts for 0.13% of births.
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.