Contra Costa County Incorporated February 18, 1850 as one of the original 27 counties created by the California legislature on that date. In 1853, people in the current Alameda County decided to break off from Contra Costa to form their own county out of parts of Contra Costa and Santa Clara. Citizens of the new Contra Costa went through a sometimes heated debate to decide whether or not to change the name of the county. One noteworthy proposal was "Diablo County" after the mountain, but several religious groups and prominent citizens opposed this, and the name thus remained "Contra Costa". Population (January 1, 1998): 900,700 Contra Costa is the 3rd most populous county in the San Francisco Bay Area after Santa Clara and Alameda, and the 9th most populous of the 58 counties in California. Approximately 2.7% of the people in California live in Contra Costa County. Size 733 square miles, 49th largest in California by size. Within the San Francisco Bay Area, only San Mateo County has more cities than Contra Costa County (Contra Costa: 18, San Mateo: 20). East Bay Regional Park District The East Bay Regional Park District manages 55 parks covering more than 85,000 acres and over 1,000 miles of trails, including 26 regional inter-park trails within the two East Bay counties, Contra Costa and Alameda. The East Bay Regional Park District was formed after voter approval on November 6, 1934. The idea for the organization came in 1928, when EBMUD declared surplus some 10,000 acres of former watershed lands in the East Bay hills. Bay Area Ridge Trail The Bay Area Ridge Trail Council was established in 1987 to build a 400-mile ridgeline trail connecting the Bay Area's parks and open spaces, linking hundreds of communities region-wide. The trail makes a huge oval circle around the entire Bay Area, and passes through the western and southern parts of central Contra Costa County, including parts of Martinez.