Tahquamenon Falls is the largest falls east of the Mississippi: 50 feet tall and 200 feet across. The paved trail to the upper falls is .8 miles round trip. There is a four mile trail to the lower falls, or you can drive there.
4 miles southwest of Lower Falls is the Upper Falls. They are touted as the 2nd largest waterfall east of the Mississippi. I don't know how that is measured, but they are pretty good sized (not particularly tall however. From the parking lot, you can hike a couple of short trails. One leads you to a viewpoint fairly close to the falls (see the picture.) The other is a stairway that will take you down the river gorge where you can view the falls in the distance (see my intro page). Neither is very long, although the Gorge has altitude changes, so you can probably hit both without too much effort.
There are a number of trails that go through the park. A roughly 4-mile trail connects viewpoints of the upper and lower falls. At the upper falls, there are a couple of viewpoints that you can easily walk to - one that stands overlooking the falls, while another nature trail heads down the gorge so you can see it from a distance. The trials near lower falls are paved or raised boardwalks through the forest until you hit an overlook. This was a particularly pleasant walk.