Contra Costa County is a primarily suburban county in the San Francisco Bay Area of California. As of the 2006, the US Census Bureau estimated it had a population of 1,024,319. The county seat is the city of Martinez.

This county is made up of several distinct geologic terrains, as is most of the greater San Francisco Bay Area, which is one of the most geologically complex regions in the world.
Early interaction of Native Americans with Europeans came with the Spanish colonization via the establishment of missions in this area, with the missions in San Jose, Sonoma, and San Francisco and particularly the establishment of the Presidio of San Francisco (a military establishment) in 1776.

The large and rapid population gain due to the California gold rush gave California enough population to be admitted to the Union in 1850.

Contra Costa County was one of the original counties of California, created in 1850 at the time of statehood. The county’s name means ‘opposite coast’ in Spanish. It was given because of its opposite location to San Francisco. Southern portions of the county's territory, including all of the bayside portions opposite San Francisco and northern portions of Santa Clara County, were given up to form Alameda County effective March 25, 1853.

The establishment of BART, the modernization of Highway 24, and the addition of a third Caldecott Tunnel all served to reinforce the demographic and economic trends in the Diablo area, with cities such as Walnut Creek becoming neighboring cities.

County Website: http://www.co.contra-costa.ca.us
School Districts: http://www.cccoe.k12.ca.us/about/districts.html