Known as Mill Street for the first block, NY 17B proceeds downhill and meets an intersection with the eastern end of Sullivan County Route 133 (CR 133).

The mainly rural roadway winds east for several miles, reaching the southern end of the hamlet of Hortonville.

[3] Turning further south, NY 17B continues paralleling the East Branch, passing multiple farms before making several jaunts to the southeast.

Passing several cemeteries east of Bethel, the route soon reaches the hamlet of White Lake area, intersecting with NY 55 and CR 13.

[3] After a short parallel with the Mongaup River, NY 17B continues east and soon northeast into the hamlet of Coopers Corners.

A short distance outside of Coopers Corners, the route crosses into Maplewood, entering the town of Thompson.

This accounts for the straight, wide route much more amenable to modern vehicular use than the other inland state highways in this half of the county.