Gillian has been given to about 16,127 people in the United States since 1880. It was most common in 1999, which makes it a Gen X and millennial name.
Its best year was 1999, when 1,030 babies were given the name, ranking 303rd. The typical living American called Gillian is about 27 years old today. It is relatively most common in Ohio, where it accounts for 0.01% 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.