Ainsworth was born in Springboro, Ohio on June 6 1822. His parents died while he was young, so he went to work for his uncle. They became partners in a business selling goods from boats along the Ohio River, but soon he split from his uncle and bought a store with a partner, which was sold at a good profit after only one year. He married a young woman, Josephine Augusta Kendall, who died fifteen months later. All of this took place before Ainsworth turned twenty.
Ainsworth was not done partnering with his uncle. In 1844 they bought a steamboat and started a successful packet delivery service along the upper Mississippi River. Then the Gold Rush hit in 1849, and he sold his share of the business to go to California. The Gold Rush did not live up to his expectations, so he found a job piloting a steamer on the Willamette River in Oregon.
In 1851, he married the daughter of Judge S.S. White, and built a house in Oregon City.
In late 1860, Ainsworth and several investors started the Oregon Steam Navigation Company (OSNC). The OSNC controlled the shipping routes of steamers, railroads, and freight lines in Washington and Oregon. By 1869, the OSNC monopolized the Columbia River transportation market. In April 1879, Henry Villard purchased the OSNC for its full value of $5 million. Ainsworth retired to Oak Lawn, California after the sale.
Ainsworth had four children: George, John, Harry and Daisy.
After retiring to California he wrote his autobiography.
He died in California in December 1893.