what county is colfax in
Colfax, California. Colfax (formerly, Alden Grove, Alder Grove, Illinoistown, and Upper Corral) is a city in Placer County, California, at the crossroads of Interstate 80 and State Route 174. It is part of the SacramentoâArden-ArcadeâRoseville Metropolitan Statistical Area. The population was 1,963 at the 2010 census.