2017 Population Estimate: 1,149,363. More. Unincorporated County 2018 Population Estimate: 172,513. Print. Contra Costa County Demographics 2010 Population: 1,049,025. source: 2010 Decennial Census. Department of Finance Population Estimates of Cities, County, and the State. Map. Embed. Chart. Name Status County Population Census 2000-04-01 Population Census 2010-04-01 … Dashboard. Email. Contra Costa County, California's estimated population is 1,160,920 with a growth rate of … CSV. QuickFacts provides statistics for all states and counties, and for cities and towns with a population of 5,000 or more. Contra Costa County, California. Clear 1 Table. Source: 2018 California Department of Finance.