[2] The freeway travels northeast through the Rathdrum Prairie and into the outskirts of Post Falls, passing several retailers and a business park along the Spokane River.

I-90 continues east along the river, paralleled to the south by the North Idaho Centennial Trail and a section of the BNSF Railway, and passes near the eponymous Post Falls and the city's downtown, served by a signed business route.

The freeway intersects State Highway 41 (SH-41) and continues through the city's eastern residential neighborhoods and passes the nearby town of Huetter.

I-90 then reaches Coeur d'Alene, the largest city in northern Idaho, and intersects a business route and US-95, the state's main north–south highway, near the Kootenai Medical Center.

I-90 continues east along Cedar Creek into the Coeur d'Alene Mountains, part of a national forest,[3] and reaches Fourth of July Summit at an elevation of 3,173 feet (967 m).

[5] From the summit, I-90 continues southeast along Fourth of July Canyon towards the Coeur d'Alene River valley and intersects SH-3 near Rose Lake.

The freeway turns east in the town of Wallace, also served by its own business route, and travels to the north of downtown on an elevated viaduct cut into a nearby hill.

The highway continues along the south side of the river and Trail of the Coeur d'Alenes as it ascends further into the mountains and meanders around hills and gulches.

The freeway travels uphill from the river along a southern ridge and passes a scenic viewpoint commemorating the 1903 Willow Creek avalanche.

[26][27] The link from Post Falls to the Washington state border was completed in 1972 at a cost of $1.1 million to upgrade the existing road and build a new bridge over the Spokane River.

Before the move to the viaduct, I-90 went from a freeway at the western edge of Wallace, then turned to surface streets and followed the main arterial as U.S. Route 10 through town, which included the last stoplight on I-90 between Seattle and Boston.