According to the U.S. Census Bureau Los Angeles County (California) is the most populous county in the country, with a total population of more than 10 million. Cook County in Chicago follows (~5 million residents). In Texas, Harris County, Maricopa County in Arizona, and San Diego County and Orange County in California have populations above 3 million. In the U.S. there are 45 counties with a population of more than 1 million.