Colby is at (39.392093, -101.047532). It has an elevation of 3,159 feet (963 m). It is on the south side of Prairie Dog Creek. Prairie Dog Creek is a tributary of the Republican River. It is in the High Plains region of the Great Plains. A small tributary of the creek flows northeast through the town. It is at the interchange of Interstate 70 and K-25 in northwestern Kansas. Colby is east-southeast of Denver, northwest of Wichita, and west of Kansas City.