Yes, on a clear day, you can see parts of Michigan from the Willis Tower's Skydeck. The 1,451-foot (442 m) skyscraper—still commonly called the Sears Tower—stands about 40 miles (64 km) from the Michigan state line across Lake Michigan.
Crystal-clear, low-humidity days—especially in autumn or after a cold front—offer the best chances. Haze, humidity, and lake-effect clouds frequently obscure the view. The curvature of the Earth limits visibility to roughly 45–50 miles from that height, so only the nearest slice of Michigan is visible.
The Willis Tower's Skydeck attracts 1.7 million visitors annually. On exceptionally clear days, four states are theoretically visible: Illinois, Indiana, Wisconsin, and Michigan.