Only Lake Michigan is entirely within US borders.
What is the great lake that covers most of the US?
Lake Michigan
That would be Lake Michigan, the one by Chicago IL. Although not the largest of the 5 Great Lakes (that would be Lake Superior), Lake Michigan is the only one of the 5 that is entirely located within the boundaries of the USA. The other 4 lakes are half in Canada, and half in the US, with the boundary between the two countries dividing each lake.
Lake Michigan is the only Great Lake entirely within the US. The other 4 great lakes are on the border.
Your question assumes the Great Salt Lake is the largest lake in the US. It is not. That would be Lake Superior.
The largest lake totally in the United States is Lake Michigan at 22,400 square miles. Excluding the Great Lakes, Great Salt Lake in Utah could be the largest lake at 1700 square miles.
Lake Michigan
Lake Michigan is the only one of the Great Lakes that is entirely within the US boundaries. All the other lakes have split boundaries with Canada. Lake Michigan is between the states of Michigan on the east and Illinois and Wisconsin on the west.
Lake Michigan is entirely in the US
Lake Michigan is the only Great Lake that is not shared with Canada.
The Great Salt Lake.