Cotopaxi is a census-designated place and U.S. post office in Fremont County, Colorado, United States. The population as of the 2010 census was 47, 44 of whom were non-Hispanic white people. The Cotopaxi Post Office has the ZIP code 81223. It was a small train stop on the Denver and Rio Grande Western Railroad along the Arkansas River. Though there is a store serving the main highway through the town (U.S. 50), there are no major businesses in Cotopaxi (owing to the small population) except for a whitewater rafting business that attracts thousands of tourists each year to ride on the Arkansas River.