This is the go-to running destination in the Litchfield Hills, and for good reason. The Farmington Canal Heritage Trail is a mostly paved multi-use path that stretches roughly 40 miles between Suffield in the north and Southington in the south. The path is geneally flat and scenic as it winds along the river, with access points in several towns including Simsbury, Avon, Collinsville, Unionville, Plainville, and Southington. The northern section of the path follows Rt. 202 for several miles. There are mileage markers along the trails.
The Farmington River Trail branches off to the west at the southern end and follows the Farmington River for 16 miles, rejoining the Heritage Trail in Simsbury (11.2 mile marker). It is stone dust for about 1/4 of its length and has a 3-mile on-road section. The northern and southern trail maps have excellent info on distances and parking.
Eventually, a proposed route will connect the southern section of the trail to New Haven, CT and the northern section to Northampton, MA.