Hardin was elected secretary of the ayuntamiento of Liberty in 1831 and was surveyor of the Atascosita District from 1834 to 1836. He was first lieutenant of infantry and fought in the siege of Bexar under Col. Francis White Johnson. Hardin served as a lieutenant in Capt. William M. Logan's company until June 1836. He carried the San Jacinto victory dispatch for Sam Houston to the United States border. Between July 7, 1836, and October 7, 1836, he was captain of a newly organized company and joined an expedition against the Indians. Hardin was put in charge of guarding Mexican officers interned at his brother's plantation until they were repatriated in 1837. He was Liberty county surveyor (1838-45) and served as colonel of the Second Brigade of the Texas militia (1842-43). In 1839 he was appointed postmaster by Sam Houston and moved his family from his plantation north of Liberty to a house in town, known as Seven Pines, where he lived with his wife and six children and a slave known as Aunt Harriet. Harriet had moved to Texas with the Hardins in 1826 and lived to be nearly 100 years old.
Hardin continued to live near Liberty, where he was district surveyor from 1849 to 1852. He served in the Texas legislature in 1857, when Hardin County was formed from Liberty County and named in honor of the Hardin family. In the legislature he helped to get a surveyors' bill passed and the University of Texas founded and served as chairman of the Public Lands Committee. He married Cynthia O'Brien in 1839; they had six children. Hardin was a Methodist. He died at his residence in Liberty on April 21, 1878. State historical markers were placed at the Hardin family cemetery in 1936 and the Liberty home site, Seven Pines, in 1988.
30° 03.791, -094° 48.168