Barnum was born in Bethel, Connecticut, the son of inn keeper, tailor and store-keeper Philo Barnum (1778-1826) and second wife Irene Taylor, who had ten children. He was the third great grandson of Thomas Barnum (1625-1695), the immigrant ancestor of the Barnum family in North America. His maternal grandfather Phineas Taylor was a whig, legislator, landowner, justice of the peace, and lottery schemer, and he had a great influence on his favorite grandson. Barnum was adept at arithmetic but hated physical work. Barnum started as a store-keeper, and he learned haggling, striking a bargain, and using deception to make a sale. He was involved with the lottery mania in the United States. He married Charity Hallett when he was 19; she'd be his companion for the next 44 years.
The young husband had several businesses: a general store, a book auctioning trade, real estate speculation, and a state-wide lottery network. He became active in local politics and advocated against blue laws promulgated by Calvinists who sought to restrict gambling and travel. Barnum started a weekly paper in 1829, The Herald of Freedom, in Danbury, Connecticut. His editorials against church elders led to libel suits and a prosecution which resulted in imprisonment for two months, but he became a champion of the liberal movement upon his release. In 1834, when lotteries were banned in Connecticut, cutting off his main income, Barnum sold his store and moved to New York City.