| State: | ID |
| Type: | SH |
| Route: | 66 |
| Map Custom: | yes |
| Map Notes: | SH-66 highlighted in red |
| Maint: | ITD |
| Length Mi: | 0.992 |
| Length Round: | 3 |
| Length Ref: | [1] |
| Direction A: | West |
| Terminus A: | Palouse Cove Road at Washington state line |
| Direction B: | East |
| Terminus B: | near Viola |
| Counties: | Latah |
| Previous Type: | SH |
| Previous Route: | 64 |
| Next Type: | SH |
| Next Route: | 67 |
State Highway 66 (SH-66) is a state highway located entirely within Latah County, Idaho, United States. It travels for less than 1miles from Palouse Cove Road at the Washington state line to U.S. Route 95 (US-95) north of Viola. The highway is maintained by the Idaho Transportation Department.
SH-66 begins at the Washington state line as a continuation Palouse Cove Road, which connects to the city of Palouse. From the state line, the highway travels southeast through a rural area and turns east to reach its terminus at US-95 north of Viola. The route is a two-lane undivided road for its entire length.