Politician. He represented Clay County in the Missouri House of Representatives, from 1824 to 1832, serving as Speaker of the House, 1828 to 1830. In 1834 he served at the rank of colonel in the Clay County militia, commanding the 28th Regiment, 3rd Brigade, 1st Division and fighting in Native American uprisings along the western border of the state. He was reelected to the Missouri General Assembly in 1836. He was the oldest son of five children of William Thornton and Sarah Jane Allison, who immigrated from County Donegal, Ireland during the American Revolutionary War. Born in Pennsylvania, he moved to Kentucky around 1795, where he studied law and was accepted to the bar. In 1816, he moved to Missouri before it was a state, first to Howard County and later to Clay County. He built the "Western Farms Plantation" and operated a ferry in Jackson and Clay counties. Eventually, most of his siblings came to Missouri and his youngest brother became a judge in a neighboring county. By 1836 there was a settlement of hundreds of members of the Church of Jesus Christ of Latter-day Saints, or Mormons, in Jackson County. Other citizens were demanding that the Mormon group must leave the area. Since the Mormons were abolitionists and defended the land rights of Native Americans, they were being persecuted for their beliefs. Thornton and his son-in-law Alexander Doniphan, who was the defense attorney for Mormon Prophet Joseph Smith, attempted to resolve the situation without any violence from a mob. At one point the state militia was summoned to fight against the Mormons thus the 1838 Mormon War. While serving in the militia, Doniphan saved Smith from being executed saying it "would be cold blooded murder." On October 27, 1838, the governor issued the Mormon Extermination Order #44. The Mormons did leave from Jackson County to Clay County and eventually, left the state. Letters concerning this matter have been archived in "The Joseph Smith Papers," which are online. For being such an interesting well-respected man, his obituary from the "Liberty Tribune" dated, Sunday, October 31, 1847 simply read: "Colonel John Thornton died on Sunday morning, aged nearly 61 years."