| State: | WI |
| Type: | WI 1949 |
| Route: | 166 |
| Alternate Name: | Fond du Lac Avenue |
| Established: | 1927 |
| Deleted: | 1953 |
| Maint: | none |
| Length Mi: | 2.1 |
| Direction A: | South |
| Direction B: | North |
| Terminus B: | in Menomonee Falls |
| Previous Type: | WI |
| Previous Route: | 165 |
| Next Type: | WI |
| Next Route: | 167 |
Wisconsin Highway 166 (WIS 166) was a state highway in the Milwaukee metropolitan area in Wisconsin. The route traveled in a southeast–northwest direction from US 45/WIS 55 to WIS 74 in Menomonee Falls (now just Main Street). WIS 166 was removed in 1953 when US 41 moved over.
Starting at US 45/WIS 55 (now WIS 145), WIS 166 traveled northwest along Fond du Lac Avenue. After 2.1miles, the route ended at WIS 74 (Main Street) in Menomonee Falls.[1]
In 1926, WIS 55 moved north along WIS 155 to bypass Menomonee Falls; WIS 155 was subsequently removed and WIS 165 was formed along the northern part of the former alignment of WIS 55, located north of Menomonee Falls.[2] About a year after the realignment, WIS 166 was formed along the southern part of the same former alignment, located south of Menomonee Falls.[3] WIS 166 was removed in 1953 after US 41 moved north along a newly built divided highway, which was situated just north of WIS 166.[4] [5]