Highlands Ranch is an unincorporated community and a Census Designated Place located in Douglas County, Colorado, United States. The estimated population was 128,273 in 2007, making Highlands Ranch one of the most populous unincorporated communities in the United States. The Littleton Post Office serves Highlands Ranch. Highlands Ranch apartments for rent comparison page shows most up to date rent information on Highlands Ranch apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.