Suffolk County is located in the Commonwealth of Massachusetts, in the United States. As of the 2020 census, the population was 797,936, making it the fourth-most populous county in Massachusetts. The county comprises the cities of Boston, Chelsea, Revere, and Winthrop. The traditional county seat is Boston, the state capital and the largest city in Massachusetts. The county government was abolished in 1999, and so Suffolk County today functions only as an administrative subdivision of state government and a set of communities grouped together for some statistical purposes. Suffolk County is located at the core of the Boston-Cambridge-Newton, MA-NH Metropolitan Statistical Area as well as the greater Boston-Worcester-Providence, MA-RI-NH-CT Combined Statistical Area.

Massachusetts, officially the Commonwealth of Massachusetts, is a state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and Gulf of Maine to its east, Connecticut and Rhode Island to its south, New Hampshire and Vermont to its north, and New York to its west. Massachusetts is the sixth-smallest state by land area. With over seven million residents as of 2020, it is the most populous state in New England, the 16th-most-populous in the country, and the third-most densely populated, after New Jersey and Rhode Island.