[2] WIS 66 originally began at the corner of Reserve and Main streets in downtown Stevens Point however once US Highway 10 (US 10) finished the expansion of the bypass around Stevens Point deserting the old US 10, plans arose to expand WIS 66 to use the former highway.

This is how WIS 66 got its current-day route, which begins in Wisconsin Rapids traveling east on the Old CTH-P, it then adjoins the former US 10 which routes through downtown Stevens Point, passing the University of Wisconsin–Stevens Point campus, and later joins with current US 10, US 51, and Interstate 39 (I-39) traveling north.

WIS 66 then departs from I-39/US 10/US 51 and continues northwest past the Stevens Point Municipal Airport, heading east at Jordan near the Jordan County Park of Portage County.

After crossing CTH-J near the unincorporated town of Ellis, WIS 66 turns northwest again to Rosholt, where it becomes Grand Avenue.

Initially, WIS 66 used to be on the other side of the Wisconsin River.