Colin Jost was born and raised in the Grymes Hill neighborhood of Staten Island, New York. He has one brother, Casey Jost, who had a role in Staten Island Summer and is a writer for Impractical Jokers. His mother, Kerry J. Kelly, was the chief medical officer for the New York City Fire Department, and his father, Daniel A. Jost, is a former teacher at Staten Island Technical High School. Jost was raised Roman Catholic. He attended Regis High School in Manhattan, where he was the editor of the school newspaper The Owl, and Harvard University, where he was president of the Harvard Lampoon. During his freshman year there, he lived in Greenough Hall.