Sebago Lake (Sih-Bay-Goh) is the deepest and second-largest lake in the U.S. state of Maine. The lake is 316 feet (96 m) deep at its deepest point, with a mean depth of 101 feet (31 m). It is possible that Sebago is the deepest lake wholly contained within the entire New England region, although some sources say that Vermont's Lake Willoughby is slightly deeper. Along with Lake Champlain, Sebago is one of the only lakes in the area that does not consistently freeze solid during the winter months, with total ice cover only occurring for a short period of time every few winters. Sebago covers about 45 square miles (117 km2) in surface area, has a length of 14 miles (23 km) and has a shoreline length of roughly 105 miles (169 km). The surface is around 270 feet (82 m) above sea level, so the deep bottom is below the present sea level. It is in Cumberland County, and bordered by the towns of Casco, Naples, Raymond, Sebago, Standish and Windham. The seasonally occupied town of Frye Island is on an island in the lake. Sebago Lake and the surrounding area is known for its erratic and sudden changes in weather during all seasons, likely due to its proximity to the Atlantic Ocean and to Mt. Washington, a very notorious extreme weather hotspot. The name comes from the Abenaki sobagoo, meaning "it is the sea" or "it resembles the sea".

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.