Essex County is a county in the northeastern part of the U.S. state of Massachusetts. At the 2020 census, the total population was 809,829, making it the third-most populous county in the state, and the seventy-eighth-most populous in the country. It is part of the Greater Boston area. The largest city in Essex County is Lynn. The county was named after the English county of Essex. It has two traditional county seats: Salem and Lawrence.