The Toledo War of 1835 involved a confict between the United State of Ohio and the Territory of Michigan over the city of Toledo.

Due to inaccurate land surveys in the early 19th century the southern tip of Lake Michigan was described as being in two different locations. Michigan's land grant stated that all of the land down to the southern tip of Lake Michigan belonged to the Territory of Michigan. Michigan claimed the southern line was correct, while Ohio claimed the northern line was correct. This discrepancy resulted in a strip of disputed land known as the Toledo Strip. Toledo was the only city of note contained within the strip.

When it came time for Michigan to gain statehood, its borders had to be established. Michigan and Ohio could not compromise and Ohio's Governor Robert Lucas drew counties and set up county governments in the strip. Toledo was placed within Lucas County of Ohio, named after the Governor. Michigan's nineteen-year-old territorial governor Stephens T. Mason responded by sending a militia force to the area. Lucas did the same. The Toledo Strip was at the time covered with dense cedar swamps (collectively known as the "Black Swamp"), which today have almost all been drained off for farm land. The two armies got lost for weeks and never found each other in the swamps. The United States Congress settled the issue by awarding Toledo to Ohio and giving Michigan the western two-thirds of the upper peninsula (the eastern portion was already part of the Territory). Ohio was considered the winner at the time because the "U.P." was thought to be worthless; only later was the extent of its rich mineral resources known.

See also: Military history