Pacheco is a census-designated place (CDP) in Contra Costa County, California. The population was 3,685 at the 2010 census. It is bounded by Martinez to the north and west, Concord to the east, and Pleasant Hill to the south.

Contra Costa County is a county located in the U.S. state of California, in the East Bay of the San Francisco Bay Area. As of the 2020 United States Census, the population was 1,165,927. The county seat is Martinez. It occupies the northern portion of the East Bay region of the San Francisco Bay Area and is primarily suburban. The county's name refers to its position on the other side of the bay from San Francisco. Contra Costa County is included in the San Francisco–Oakland–Berkeley, CA Metropolitan Statistical Area.