Peter Hubbard posted the route:
Using the Manistee River Trail (MRT) from the Seaton Creek Campground and connecting it with the North Country Trail (NCT) makes a 23 mile loop. Below is a link to a trail map and my splits. It's a very scenic trail, I haven't found anyone who has run it, but it's a popular backpacking loop. I highly recommend it as a moderately challenging trail run to anyone in the area or passing through.
Seaton Creek Campground to Suspension Bridge (1.4 miles)
Suspension Bridge to Red Bridge via MRT (9.6 miles)
Red Bridge to Suspension Bridge via NCT (10.6 miles)
Suspension Bridge to Seaton Creek Campground (1.4 miles)
Thanks for posting this Peter! I'm looking to run the loop next weekend (6/29/18 and 6/30/18), starting from the Red Bridge trailhead and ending at the Red Bridge on the opposite side (East side), since the bridge is out for construction currently. Just checking Strava, I see there is a segment established for the loop using the same starting and ending points that I'm planning to run. It looks like it differs slightly from your original route, as it cuts out the little out and back to and from Seaton Creek Campground. Is this the proper way to run it, cutting out the campground out and back section? It seems like it would make it more accessible to start the FKT from any point, so long as you complete the loop and finish where you started. Just a thought! You could cut out your splits for that little section, and I think you would still have the FKT. It looks like the Strava segment leader (as of 6/24/18) currently has the course record at 3:19:53.
I am going to be heading to run the Manistee River Trail Loop for the female FKT November 3, 2018. I will be starting at the Seaton Creek Campground as the 1.4 mile out/back is the history of the loop, so I will stick to that instead of just doing the loop that is on Strava.
Visiting Michigan, so going to take shot at finding this loop tomorrow and doing an unsupported attempt.