Michigan has the longest freshwater coastline in the US and the second longest coast line in the US next to Alaska.
There is a comparative table of state shorelines on the Michigan Dept. of Environmental Quality's site that gives the measurements for states touching the Great Lakes. See http://www.michigan.gov/deq/0,1607,7-135-3313_3677-15959--,00.html
World Book Encyclopedia (v.13, p.500 of the 2000 edition) states that Michigan's shoreline, at 3,288 miles is "more than any other state except Alaska. This includes 1,056 miles (1,699 kilometers) of island shoreline." In v.1 (p.284 and 294) of the same edition it states that Alaska has 6,640 miles or 10,686 kilometers of coastline.