Larimer County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 359,066. The county seat and most populous city is Fort Collins. The county was named for William Larimer, Jr., the founder of Denver.

Colorado is a landlocked state in the Mountain West subregion of the Western United States. Colorado borders Wyoming to the north, Nebraska to the northeast, Kansas to the east, Oklahoma to the southeast, New Mexico to the south, Utah to the west, and meets Arizona to the southwest at the Four Corners. Colorado is noted for its landscape of mountains, forests, high plains, mesas, canyons, plateaus, rivers, and desert lands. Colorado is one of the Mountain States and is often considered to be part of the southwestern United States. The high plains of Colorado may be considered a part of the midwestern United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. Colorado is the eighth most extensive and 21st most populous U.S. state. The United States Census Bureau estimated the population of Colorado at 5,877,610 as of July 1, 2023, a 1.80% increase since the 2020 United States census.