William Hardin, early settler, lawyer, and judge, third son of Swan and Jerusha (Blackburn) Hardin, was born in Franklin County, Georgia, on March 25, 1801. In the early 1800s, possibly by 1807, the family moved to Maury County, Tennessee, and by 1825 Hardin was the editor of the Columbia (Tennessee) Reporter and was practicing law. Irate about an affair between his brother's wife, Mrs. A. B. Hardin, and Isaac Newton Porter, of which Porter bragged publicly, Hardin accompanied his brothers to a meeting with Porter and William Williamson in Columbia, Tennessee, on October 1, 1825. During the confrontation that developed, his brothers, Augustine and Benjamin Franklin Hardin, fatally shot Porter and Williamson. After being indicted with his brothers in December 1825, William traveled to what is now Liberty County, Texas, by 1827, in order to avoid a possible conviction for murder and to join other family members. The governor of Tennessee issued extradition papers for Hardin, who was arrested and held in San Antonio but escaped. After he was arrested again, José Francisco Ruiz took him to Nacogdoches, where Hardin again escaped. He returned to Liberty County and in 1829 married Sarah Loony; they had two children.
In May 1831 Hardin was elected commissary of police in Anahuac. He also served as secretary of the board for the town of Liberty for 1831. During the Anahuac Disturbances of 1831–32 he was a leader of the colonists. In March 1832 he was elected alcalde of Anahuac. He assisted with the setting of the cornerstone of Fort Anahuac on May 14. He maintained residences in Liberty and Anahuac from 1831 to 1836, practiced law, and speculated heavily in Texas lands, especially with the Galveston Bay and Texas Land Company. He served as a delegate to the Convention of 1833 in San Felipe de Austin. In 1835 he was elected alcalde of Liberty. He served as postmaster and the first judge for the jurisdiction of Liberty in 1836. After the battle of San Jacinto he housed Mexican officers, including Gen. Martín Perfecto de Cos, as prisoners until 1837 at his Liberty plantation, thereafter known as Mexican Hill. In 1838 Hardin was one of the original ten proprietors of the city of Galveston, where he also established a residence. In 1839 he was reappointed as Liberty postmaster.
He died of yellow fever on June 28, 1839, in Galveston, and his body was shipped via sailboat to Liberty for his funeral. He was buried in the Hardin family cemetery north of Liberty. At the time of his death he was one of the wealthiest men in Texas, with an estate including 114,222 acres and thirty-two Galveston city lots. The Texas Centennial Commission placed a monument at his grave in 1936, and the Liberty County Historical Commission obtained a state historical marker for the site of Mexican Hill in 1983. Hardin County and Hardin, Texas (Liberty County), were named in honor of the Hardin family of Liberty.