Maine's 1st congressional district is a congressional district in the U.S. state of Maine. The geographically smaller of the state's two congressional districts, the district covers the southern coastal area of the state. The district consists of all of Cumberland, Knox, Lincoln, Sagadahoc, and York counties and most of Kennebec County. Located within the district are the cities of Portland, Brunswick, and Saco. The district is currently represented by Democrat Chellie Pingree.

Cumberland County is a county in the U.S. state of Maine. As of the 2020 census, the population was 303,069, making it the most populous county in Maine. Its county seat is Portland. Cumberland County was founded in 1760 from a portion of York County, Province of Massachusetts Bay, and named for William, Duke of Cumberland, a son of King George II. Cumberland County has the deepest and second-largest body of water in the state, Sebago Lake, which supplies tap water to most of the county. The county is the state's economic and industrial center, having the resources of the Port of Portland, the Maine Mall, and having corporate headquarters of major companies such as Fairchild Semiconductor, IDEXX Laboratories, Unum, and TD Bank. Cumberland County is part of the Portland–South Portland, ME Metropolitan Statistical Area.