Winthrop is a town in Suffolk County, Massachusetts, United States. The population was 19,316 at the 2020 census. Winthrop is an ocean-side suburban community in Greater Boston situated at the north entrance to Boston Harbor, close to Logan International Airport. It is located on a peninsula, 1.6 square miles (4.2 km2) in area, connected to Revere by a narrow isthmus and to multiple portions of Boston by a bridge over the harbor inlet to the Belle Isle Marsh Reservation in the Neighborhood of East Boston, a shared border at the Boston Logan International Airport, and at Deer Island.

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.