Harrison remained in the army until May 31, 1798, rising to the rank of captain. After resigning from the army, Harrison moved his family down the river to North Bend, Ohio. Harrison purchased 160 acres of land for $450.


June 28, 1798 President John Adams appointed Harrison Secretary of the Northwest Territory, and the following year (1799-1800) he was Territorial Delegate to Congress. Harrison's Land Act of 1800 freed the settlers from dependance on land speculators by providing for the purchase of small tracts with liberal credit.


Harrison served, at President Adams' appointment, as the Territorial Governor of Indiana from January 1801 to December 1812. These were the most satisfying years of his life. It was during this time he moved his family to Vincennes, the territorial capital, and built Grouseland on the Wabash River.