Where was the northernmost battle during the Civil War?

    The northernmost battle of the Civil War was fought in St. Albans, Vermont, on October 19, 1864. A group of 22 Confederate soldiers, led by Lt. Bennet H. Young, crossed from Canada into St. Albans, shot up the town, and robbed three banks of more than $200,000. They attempted to burn the village, but townspeople prevented this destruction. Eleven members of the group escaped back into Canada where they were arrested and later released.
    The northernmost naval engagement was the Battle of Portland, Maine, on June 27, 1863. There were two fights in Ohio--the Battles of Buffington's Island and Salineville.
    On a grander scale, the Battle of Gettysburg (Pennsylvania) was the northernmost major engagement. There were several battles in Maryland (Antietam, Monocacy, South Mountain, Crampton's Gap), and the Battle of Fort Stevens was fought within the District of Columbia.

(from The Civil War Day By Day)