Mariposa County is a county in the U.S. state of California, located in the western foothills of the Sierra Nevada mountains. It lies north of Fresno, east of Merced, and southeast of Stockton. As of 2000, its population was 17,130. The county seat is Mariposa.The county's eastern half is the central portion of Yosemite National Park.

There are no incorporated cities in Mariposa County; however, there are three communities recognized as census-designated places for statistical purposes. It also has the distinction of having no permanent traffic lights anywhere in the county. Mariposa County was one of the original counties of California, created at the time of statehood in 1850. While it began as the state's largest county, over time territory that was once part of Mariposa was ceded to twelve other counties: