Kolby is a spelling variant of Colby, an English place name and surname from the Old Norse that means "Koli's farm", Koli being a nickname for a dark-haired or swarthy man. The K spelling peaked in the United States around the same time as Kolton and Kody. Kolby ranked number 542 in 2000, peaked at 359 in 2001, dropped out of the top 1000 in 2017 and ranks 1225 in 2025.