Which lake is the largest lake in the United States by surface area?

Lake Superior is the largest lake in the United States by surface area.

Although it is shared with Canada, Lake Superior has the greatest surface area of any lake bordering the United States, about 82,100 square kilometres overall. Its international boundary runs through the lake, with Ontario to the north and the states of Minnesota, Wisconsin, and Michigan to the south and east.

Superior is also the largest freshwater lake by surface area in the world. It stores an enormous volume of cold water and has a long water-retention time, meaning water can remain in the basin for roughly two centuries before leaving through the St. Marys River.

Lake Michigan is entirely within the United States and is the country's largest lake wholly within its borders. That distinction is different from being the largest lake bordering the United States, which is why Lake Superior is the correct answer here.