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, most of whom are Caucasian. 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.