Leyner is an unincorporated community and a census-designated place (CDP) located in and governed by Boulder County, Colorado, United States. The CDP is a part of the Boulder, CO Metropolitan Statistical Area. The Lafayette post office serves the area. The Leyner CDP has an area of 151 acres (0.612 km2), including 26 acres (0.106 km2) of water.
Leyner is located in eastern Boulder County along the west side of U.S. Route 287, 4 miles (6 km) north of Lafayette. Boulder Creek forms the northern edge of the CDP. It borders Erie to the west.
Leyner is mostly residential with only a few businesses far and in between such as Academy Stables Inc, Carlisle Equestrian Center, Rock Products of Colorado – Goose Haven, and Cottonwood Farms. Leyner is served by Alexander Dawson High School and has a sports field called Alexander Dawson Sports Fields.