Ellroy-Sparta Trail
Dating from 1967, the grandfather of US bike trails!
I've ridden the 4 Trails Tour (101 miles). Not very long, but...
Compared to a typical road tour, that's very true, but we are kind of talking about trails here. It's short compared to the Katy (240 miles) or GAP (150 miles). However, it's on the long side as rail trails go, and comparable to the Mickelson (114 miles), Silver Comet & Chief Ladiga (95 miles), Paul Bunyon (115 miles), and longer than the well-known Montour (47 miles), Coeur d'Alenes (73 miles) and Little Miami (78 miles).
The 250-mile-long Florida C to C is "88% complete". The 326-mile-long Ohio to Eire is 90% segregated path.