Route 122A heads westward, crossing the Blackstone River and following it through the northwest corner of Sutton and into Millbury.

In Millbury, Route 122A crosses the river again, passing through the center of town before meeting Route 146, near the Shoppes at Blackstone Valley shopping center.

In Worcester, Route 122A leaves Route 146 at Providence Street, following it and Winthrop Street until crossing I-290 at Exit 13.

It continues northward, passing Eagle Lake and Stump Pond before meeting the southern end of Route 68.

Route 122A bends westward into the town of Rutland, where it shares a short concurrency with Route 56 before finally ending at its parent route once more, in Rutland State Park.