From the website http://warnertrail.org/
"The Warner Trail offers delightful and varied outdoor experiences as it stretches more than 30 miles from Sharon, Massachusetts, to the Diamond Hill State Park in Cumberland, Rhode Island. The trail passes through Sharon, Foxboro, Wrentham and Plainville in Massachusetts and through Cumberland, RI."
A Guide Book with detailed description of the route can be found at the above website.
Steve Levandosky created a Google map of the route as well: https://www.google.com/maps/d/u/1/edit?hl=en&mid=1ivRnG4uPcXMUgOiUpDZLt08BRiAPql6h&ll=42.070695190352055%2C-71.29695655829596&z=12
The trail is quite difficult to follow in many places. The guide book has very detailed turn by turn directions. There is a typo in the guide book on page 4, saying to turn right on Norwood, where the trail actually goes left.