The Patriot War was a short-lived campaign in the eastern Michigan area of the United States and the Windsor, Ontario area of Canada. A group of men of Irish descent on both sides of the border, calling themselves "Patriots," formed small militias in 1837 with the intention of seizing the peninsula of Canada between the Detroit and Niagara rivers. They based groups in Michigan at Fort Gratiot (present Port Huron), Mount Clemens, Detroit, and Gibraltar. In the winter of 1837 they attempted to seize the arsenal at Fort Gratiot but were stopped by state militia.

In December, the Patriots crossed the Detroit River into Canada by steamboat and engaged in an unsuccessful battle at Windsor. In 1838, Michigan militia were stationed at the United States Arsenal in Dearborn, and were used to track down remaining groups of Patriots in the area. This conflict led to the reorganization of the Michigan militia because its structure was found to be insufficient to deal with such rebellions.

These events occurred contemporaneously with the Upper Canada Rebellion and the Patriotes Rebellion further east in Canada.