idaho state highway 28 begins at an intersection with u.s. route 93 in the community of salmon. the highway proceeds southeast through the lemhi valley, traveling parallel to the lemhi river for several miles. the road passes through leadore, intersecting idaho state highway 29 while in the community. just after exiting the town, the highway passes the leadore airport. the roadway continues southeastward for a short distance before bending south and proceeding through the lemhi valley. after a long distance, the route bends back southeastward, proceeding to an intersection with state highway 22. the route continues southeast before passing the mud lake airport, and intersecting id 33. the road runs concurrently for several miles, traveling eastward. the highway bends southeast, and reaches its western terminus, an interchange with interstate 15. the entire length of the route is designated as the sacajawea historic byway by the state of idaho.