After the second curve the route leaves Zanesville, running parallel to the Muskingum River and an Ohio Central Railroad track.

The road makes a sharp curve northwest and passes through a one-lane 10'11"-clearance underpass under the Ohio Central Railroad track.

After leaving the state forest nursery, the highway passes through farmland heading due north.

The route curves northeast passing through the state forest nursery for the last time and the highway has an intersection with County Road 40 (CR 40), in rural Jefferson Township.

[9] SR 666 was established in 1937 along the same alignment between Zanesville and near Dresden within Muskingum County that it utilizes today.