Brookside is a Statutory Town located in Fremont County, Colorado, United States. The town population was 236 at the 2020 United States census. The Brookside, Colorado, post office operated from May 21, 1888, until March 15, 1909. The Town of Brookside was incorporated in 1913. Brookside postal addresses are now served by the Cañon City, Color…Brookside is a Statutory Town located in Fremont County, Colorado, United States. The town population was 236 at the 2020 United States census. The Brookside, Colorado, post office operated from May 21, 1888, until March 15, 1909. The Town of Brookside was incorporated in 1913. Brookside postal addresses are now served by the Cañon City, Colorado post office.