Hardin later moved to Frankfort and was elected to the Kentucky House to represent Franklin County.

Concurrent with his service, he participated in the War of 1812, serving alongside future Kentucky Governor George Madison as majors in Colonel John Allen's militia unit.

Following the expiration of his term as Secretary of State, Governor Gabriel Slaughter appointed Hardin to the U.S. Senate seat vacated by William T. Barry, who resigned.

[3] The Hardin family moved to Kentucky in April 1786, settling near the present-day city of Springfield in Washington (then Nelson) County.

[5] Among those who read law in his office were his cousin, U.S. Representative Benjamin Hardin; and future Kentucky Governor and Postmaster General Charles A.

[9] In a 1920 essay, William Barton opines that Hardin's paternity was unlikely since both he and Hanks were married at the time, and because Hardin's usual travels – to his law practice in Richmond and to state business in Frankfort – took him in the opposite direction of Nancy Hanks-Lincoln's house.

[9] The rumor arose from an inability to locate Thomas Lincoln and Nancy Hanks' marriage license at the courthouse in Hardin County, Kentucky; the license was later found in the courthouse in Washington County, effectively discrediting the rumor.

[10] Politically, Hardin favored the construction of internal improvements at federal expense and adhered to a loose interpretation of the U.S.

[3] His entry in the 1936 Dictionary of American Biography notes that, while some of his fellow Kentuckians believed he was a Federalist, Hardin was actually a national Democrat who probably would have associated with the Whig Party had he lived long enough to see its formation.

[13] Hardin's unit pursued Tecumseh through northern Ohio and Michigan and participated in the Battle of the River Raisin.

[8][13] On November 13, 1816, Governor Gabriel Slaughter appointed Hardin to the U.S. Senate seat vacated when William T. Barry resigned.