The son of Jacob Jennings and Mary Kennedy, Jonathan Jennings was born in 1784, with the official date and location of his birth unknown to historians. His father was a doctor, in addition to being a Presbyterian missionary and ordained minister. His mother, daughter of Presbyterian minister Samuel Kennedy, had been well educated and was thought to possess a medical degree because she assisted Jonathan in his practice.
Dr. Jennings moved his family to Dunlap Creek, Pennsylvania in 1790. In 1792, Mary died and Jonathan’s older siblings, Sarah and Ebeneezer, raised him and younger sister Ann, to adulthood. His earliest studies took place at home, followed by grammar school in Canonsburg, Pennsylvania. It was during these years he made friends with two boys, who as young men became his political allies.
Completing his basic education, Jennings studied law in Washington, Pennsylvania, which was followed by a move to Steubenville, Ohio in 1806. Here he worked in the law office of his brother, Obadiah Jennings, helping him with cases Obadiah argued before the Ohio Supreme Court. Later that same year, he moved west into the Indiana Territory, settling in Vincennes, the territorial capital. In the early months of 1807, he opened his own law practice and joined the Indiana Bar in April. The territory, however, proved to be a difficult place for the young attorney to make a living, due to the scarcity of clients.
A new opportunity presented itself in July, when Nathaniel Ewing, a friend from Pennsylvania and the federal land receiver in Vincennes, approached Jennings with a job offer; that of becoming the assistant to John Badollet, who at the time was the registrar in Vincennes’ federal land office. Accepting the position, Jennings then joined Badollet in land speculations and before long, amassed significant land holdings and sizeable profits. His position in the federal land office also led to Jennings becoming one of the assistants to the clerk of the territorial legislature where he continued his speculation of public land sales.
August 1807 presented Jennings with a new position. Following the resignation of General Washington Johnston, Jennings became the appointment clerk for the Board of Trustees at Vincennes University. The president of this board was Territorial Governor William Henry Harrison, hero of the Battle of Tippecanoe. In this position, Harrison exerted a great deal of influence through his veto powers and political appointments.
Johnston’s resignation resulted from his dispute with Harrison regarding the governor’s proposal to ban French residents living in Vincennes from using the commons on the university’s campus. The board later defeated the governor’s proposal. Jennings received the position rather than Harrison supporter Henry Hurst. This enraged Harrison, who shortly thereafter resigned from the board, though he later reconsidered his decision in doing so. Harrison easily won reelection in September 1807 and was named the board’s president.
Following his resignation, Johnston authored a pamphlet in which he described the board’s proceedings. Shortly after the pamphlet’s completion, Jennings certified it without the permission or knowledge of the board. This did nothing to win him favors from Harrison. If that was not enough, Jennings soon found himself further out on the limb of disapproval with Harrison when Jonathan attempted to obtain the clerkship of the territorial legislature. Jennings dropped out of the race, leaving Floyd to be selected for the position, who later became a strong political ally of Jennings.
Moving to the eastern part of the Indiana Territory in 1808, Jennings settled in Clark County. Shortly thereafter, he was elected to be the territory’s delegate to the United States Congress. While out on the campaign trail, Jennings made a point of joining in with the farmers as they worked in an effort to befriend them. Many times he engaged them in a game of ball – making a point to let the farmers defeat him. The discussion of politics was always reserved until after quitting time. In an effort to keep his speeches short, Jennings made a point of saying he had to be somewhere else and could not speak for long. His election was a result of being able to split the pro-Harrison vote by running as an anti-Harrison candidate. Governor Harrison resigned from office in 1812 and by then, Jennings had become leader of the territorial government’s pro-statehood faction.
In December, 1815, a petition was presented by Jennings from the territorial Legislature requesting statehood for Indiana be granted. The census for that year indicated the territory’s population to be over sixty-three thousand, more than sufficient to satisfy the Ordinance of 1787. In 1816, the request was granted by Congress. Jennings was elected a delegate to the constitutional convention and his fellow delegates chose him to preside over the convention
Jennings and his political allies now controlled the territory’s assembly and dominated governmental affairs. He also played an important role in the passage of the Enabling Act during 1816. This legislation authorized the establishment of the state government and constitution of Indiana. As president of Indiana’s constitutional convention, he helped draft the first constitution. He was also a strong supporter in the banning of slavery and the creation of a strong legislative branch of government.
In August, Jennings became Indiana’s first governor, serving two terms. During his time in office, he was a diligent supporter regarding the construction of schools and roads. He was also instrumental in negotiating the Treaty of St. Mary’s, which paved the way for Indiana’s central location to be opened for settlement. Opponents soon stated the actions were unconstitutional and sought to impeach him; however, after a month long investigation and resignation of the state’s lieutenant governor, Jennings remained in office by a vote of 15 to 13.
Before the end of his second term as governor in 1822 and prior to retiring from public life, Jennings served a term in the U.S. House of Representatives. While there, he promoted federal spending on internal improvements.
Over the course of his life, Jennings was a relatively heavy drinker. His alcohol addiction worsened with the death of his wife Ann and strengthened all the more with the development of rheumatism. Following his retirement from public life, Jennings’ alcoholism grew to such a degree he could no longer tend to his farm. In time, his finances collapsed and creditors arrived at the door seeking his land holdings and farm in Charlestown. U.S. Senator John Tipton, a close friend of Jennings, purchased the farm and allowed Jennings to live out the rest of his life there. Following his death, his estate was sold. Jennings’ debts were cleared in the process; however, no funds remained for a headstone to mark his grave. It would be 57 years before one was erected.