Allen County is a county located in the northwestern part of the U.S. state of Ohio. Its county seat and largest city is Lima. The county was created in 1820 and organized in 1831. The county is named in honor of Colonel John Allen, who was killed leading his men at the Battle of Frenchtown during the War of 1812.

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.