The DTE Energy Foundation Trail system (https://dtetrail.org) out by Green Lake in Waterloo has a range of trails that are very popular among the mountain biking community (which was the intended primary audience for these trails), but trail runners are most welcome too (as indicated by their website and all the cyclists that wished me a great run as I ran past them today).
Green Lake + Big Kame Loops variation (9 miles)
The original FKT consists of 2 connected loops: 1) the DTE Foundation Green Lake Loop + 2) the Big Kame loop as I found listed/described on the Trail Run Project. The Green Lake Loop is a very easy/fun/runnable 5 mile loop - and you access the other 5ish mile loop (Big Kame Trail) from within that Green Lake Loop. The Big Kame section is a bit more adventurous/slightly more technical but very runnable. As the signs clearly say - hikers/runners should run in the opposite direction from the mountain bikers (and there are a number of blind turns where it helps to shout out that a runner is coming around the corner just in case). Would definitely recommend this route, especially if you can go midweek and early in the day to avoid the crowds. Happy trails fellow Michigan trail friends!
All four loops variation (20.5 miles)
Added in May 2022 by rpkilroy. Located in the Waterloo Recreation Area (Michigan State Park), this trail currently consists of 4 distinct loops that are all connected. The trail was started in 2015 and the fourth loop was finished in 2019. The trail is primarily a mountain biking trail and has designated travel directions for bikers and foot traffic depending on the day of the week. Runners should be alert and prepared to move off trail for oncoming bikers as this single track trail has many tight turns. This route connects all four loops (Green Lake Loop, Big Kame Loop, Winn Loop, and Sugar Loop), for an approximately 20 mile run, beginning and ending at the trailhead information kiosk located in the parking area off of M-52.
I'm going to attempt the male unsupported time on Friday 5/13/22
can't make the attempt tomorrow because covid :/