Hinsdale County is one the 64 counties of the U.S. state of Colorado of the United States. As of the 2010 census, the population was 843, making it the third-least populous county in Colorado. With a population density of only 0.75 inhabitants per square mile (0.29/km²), it is also the least-densely populated county in Colorado. The county seat and only incorporated municipality in the county is Lake City. The county is named for George A. Hinsdale, a prominent pioneer and former Lt.