Get an Auto License in Colorado. Jefferson is an unincorporated town and U.S. Post Office Park County, Colorado, USA. It is located at the northern end of South Park along U.S. 285 Street, about 15 miles (24 km) northeast of Fair Play at the western foot Kenosha Pass. Which is 6 miles (10 km) from Lake Como, 23 miles (37 km) from Bailey, and 37 miles (60 km) from Breckenridge. The city consists largely of a strip of businesses along U.S. Route 285, and a small unpaved network, houses and trailers on the south side of the road. The most significant landmark of the city is a historic one room school house, visible in the meadows, and South Park. Jefferson Post Office zip code is 80456.