| State: | ID |
| Type: | SH |
| Route: | 78 |
| Maint: | ITD |
| Map Custom: | yes |
| Map Notes: | SH-78 highlighted in red |
| Length Mi: | 99.720 |
| Length Ref: | [1] |
| Direction A: | West |
| Terminus A: | in Marsing |
| Junction: |
|
| Direction B: | East |
| Terminus B: | in Hammett |
| Previous Route: | 77 |
| Next Route: | 79 |
| Previous Type: | SH |
| Next Type: | SH |
| Counties: | Owyhee, Elmore |
State Highway 78 (SH-78) is a state highway in Idaho from SH-55 in Marsing to I-84 Business Loop in Hammett
SH-78 starts at the intersection with SH-55 in Marsing and provides access to sites south of the Snake River from there to Bruneau and a few along the north side via SH-167 from Grand View. SH-78 provides access to Bruneau Dunes State Park and itself crosses the Snake into Elmore County before reaching its eastern terminus at Hammett.
The basic route of today's SH-78 from Marsing to Bruneau was in place as early as the mid-1930s, mostly as unimproved roads with a few all-weather gravel segments near Bruneau, Grand View and north of Murphy (a segment originally part of SH-45), and some paved segments near Marsing as of the 1937 map.[2]