Wordorigins.org

Columbia is a poetic name for the United States or even more broadly the Americas. It is, of course, a feminized version of the name Columbus. Use of a feminized form of Columbus’s name to refer to the new world began in England As early as the mid-17th century. Nicolas Fuller, an English clergyman, wrote in his 1660 Miscellanea Sacra:

[...] is every where called America: but according to Truth, and Desert; men should rather call it Columbina, from the magnani mous Heroe Christopher Columbus