100mi May ultramarathons in United States (Midwest)

Demanding 20-mile loop on rugged singletrack, nearly all trail with two road crossings and about 2,700 feet of elevation gain per loop.

3.0-mile loop with 237 feet of elevation gain per lap, mostly shaded gravel camp roads and trails, late May temperatures between 58 and 78 degrees

6- or 12-hour timed challenge on a 5K mixed trail and road loop with community support, crew tents, amenities, and celebratory atmosphere in the park

Looped course on scenic trails at Calvin Crest with marathon, 100-mile, and 13-hour options; cumulative elevation gains and strict Sunday cutoff

Challenging 100-mile trail course through Mohican Memorial State Forest, 95% on trails, scenic forest terrain, and multiple race distances

12.5-mile gravel road and rail-trail loop with repeated laps, regular aid access, and a low-frills, endurance-focused format