Its northern segment begins at Interstate 69 on Fort Wayne's north side, and ends at U.S. Route 20 in east-central Steuben County, approximately 6 miles (9.7 km) east of Angola.

SR 1 turns east onto US 36 for 1.01 miles (1.63 km), then leaves US 36 and travels generally due north until it reaches Fort Wayne.

On the north side of Fort Wayne at the Dupont Road interchange of Interstate 69 (I-69), the northern section of SR 1 begins and heads east.

The road heads away from I–69 as a six-lane divided highway, along the south edge of the Parkview Regional Medical Center complex, passing through numerous commercial properties.

Curving due north to enter Leo on Main Street, SR 1 then passes through residential areas of that town.

North of downtown Leo the highway curves northeast and passes through a mix of commercial and residential properties.

The route crosses CSX Railroad tracks and makes another sharp curve heading due north.

SR 1 then leaves Butler heading due north until it intersects DeKalb County Road 46, at which point the highway turns northwest.

From the present northern terminus of its southern section at Interstate 469's exit 6 in south-central Allen County, it continued north on Bluffton Road to pass just east of Fort Wayne's main airport (then known as Baer Field).

From there SR 1 headed east along Paulding Road to its intersection with US 27/US 33 (now Lafayette Street), where it turned left (north) and joined those routes to downtown Fort Wayne.