There are 9 US Post Offices in Mariposa County serving a total of 19,360 residents equating to 2,151 residents per post office. It's estimated that approximately 30,901 packages are handled across the 9 county post offices annually. Mariposa County is a county in the U.S. state of California. As of the 2010 census, the population was 18,251. The county seat is Mariposa. It is located in the western foothills of the Sierra Nevada mountains, north of Fresno, east of Merced, and southeast of Stockton. The county's eastern section is the central portion of Yosemite National Park. There are no incorporated cities in Mariposa County; however, there are communities recognized as census-designated places for statistical purposes. It also has the distinction of having no permanent traffic lights anywhere in the county."