I've been as far north as Yellow Springs.
Xenia built a replica of their old train station as a bike trail hub. The trails within a few miles of Xenia are quite urban, with a lot of street crossings.
The Little Miami State Park is the trail south from Spring Valley, following an old railroad along the Little Miami River. It's north end continues to Xenia, but that part isn't officially a state park.
The best section of the trail is from Spring Valley south to Loveland. It's often close to the Little Miami River, and much of it is wooded and shady. Most of it is not very busy. The activity picks up a few miles from Loveland, with walkers and kids on bikes, etc.
Loveland has a park adjoining the bike trail. A lot of riders start from here. There's restaurants near the trail.
The trail section to Cincinnati is scenic, but busier, with more road crossings.
Little Miami map pdf
Here's an
interactive map of the SW Ohio trails. It's a little confusing to use.
More trails info here.
Riding north to Corwin on the trail:
At Oregonia, OH:
Corwin OH trail stop: