Officials on Sunday morning listed the Hell Roaring Fire at 320 acres, up from 130 acres a day earlier.
The fire is burning in dead and downed trees about 12 miles south of Stanley.
Officials say crews put in a fire line on the western flank and completed burnouts on the southeast and northeast edges.
About 170 personnel are assigned to the blaze that started about noon on Friday. The cause of the fire is being investigated.
Some areas are closed on the west side of State Highway 75, but officials say most of the trails and recreation sites in the area are open.
No structures have been lost and none are in immediate danger.
Campers in the backcountry have been evacuated, but the majority of trails, campgrounds and recreation sites on the Sawtooth National Recreation Area remain open.
Highway 75 is also open and is expected to remain open.