Castor has been given to about 390 people in the United States since 1880. It was most common in 2016, which makes it a current name.
Its best year was 2016, when 29 babies were given the name, ranking 3702nd. The typical living American called Castor is about 10 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.