Northwest Ohio, or Northwestern Ohio, consists of multiple counties in the northwestern corner of the US state of Ohio. This area borders Lake Erie, Southeast Michigan, and northeastern Indiana. Some areas are also considered the Black Swamp area. The Toledo metropolitan area is part of the region.

Northwest Ohio's population in 2000 was 1,639,144 and is declining, specifically in the northern regions (counties shaded in the darker blue and Allen County). However, southern areas, such as Marion and Morrow counties, and the city of Findlay are growing.

Toledo is the principal city of Northwest Ohio. Most of the region's television channels and radio stations are licensed in Toledo, Perrysburg or nearby Bowling Green. Though Toledo is an industrial city, Northwest Ohio is primarily agricultural with small centers of commerce distributed across region. Since the 1970s, the population of Lucas County and the Toledo metropolitan area has declined, though Wood and Hancock counties have had moderate population growth.

These places are or may be classified as being in Northwestern Ohio, depending on the definition being applied:

If a city is a county seat, it has been listed above according to the county in which it lies. Many of the cities, townships, and villages in Northwest Ohio are clustered in the Toledo MSA. This list is incomplete.

Extreme Northwest Ohio, or Far Northwestern Ohio, is a portion of Northwest Ohio best known as the Great Black Swamp area due to its natural history. The counties of Defiance, Fulton, Henry, Paulding, Putnam, Van Wert, and Williams in the state of Ohio are usually classified as Extreme Northwest Ohio.

According to the 2000 Census, the population of this portion of NW Ohio is 234,660. When Allen and Hancock counties are included, the population is 414,428. Just like any other region, there is no universally agreed-upon line for Northwestern Ohio, as the entire area is defined differently by the opinions of multiple people.

Northwest Ohio Election Results