Eastlake is an unincorporated community and a U.S. Post Office in Adams County, Colorado, United States. The Eastlake Post Office has the ZIP Code 80614. Most of the Eastlake area has been annexed by the City of Thornton. A post office called Eastlake has been in operation since 1912. The community takes its name from nearby East Lake. The N Line ends at Eastlake.