Eldora, previously known as "Eldorado" then "El-Dora", then Eldora or Camp Eldorado, and still called Happy Valley, is an unincorporated community and a census-designated place located in and governed by Boulder County, Colorado, United States. The CDP is a part of the Boulder, CO Metropolitan Statistical Area. The population of the Eldora CDP was 140 at the United States Census 2020. The Nederland post office serves the area.