Hanover County was formed on November 26, 1720 by "An Act for Dividing New Kent County." Hanover County was named in honor of King George I, the first British monarch from the House of Hanover, who ruled over Great Britain and its colonies from 1714 to 1727.

Hanover County was the birthplace and a residence of Patrick Henry, whose concluding argument in the Parsons' Cause case of 1763 (held in the Historic Hanover Court House) may be said to have been the beginning of the American Revolution in Virginia, and made Hanover County a focal point in the Revolutionary movement.

The Hanover Tavern, Polegreen Church and Rural Plains are a few of the many Hanover landmarks that predate the Revolution, and the battles of Gaines' Mill, Totopotomoy Creek and Cold Harbor (among others) were fought in Hanover County during the Civil War.