William Alexander Richardson (January 16, 1811 – December 27, 1875) was a prominent Illinois Democratic politician before and during the American Civil War. A protege of Stephen Douglas Richardson was an ardent proponent of Jacksonian Democracy, Popular sovereignty, and Strict constructionism. During the American Civil War he initially supported the conflict, but soon became a member of the Copperhead wing of the Democratic party and a bitter critic of President Abraham Lincoln.

Born near Lexington, Kentucky, Richardson came from a distinguished family. His maternal great-grandfather was a veteran of the American Revolutionary War participating in the Battle of Kings Mountain. His maternal grandfather fought in the War of 1812 and was killed in the Battle of Frenchtown.^[1] Richardson attended Transylvania University, and then proceeded to teach school and study law. He passed the bar exam in 1831 and started his practice in Shelbyville, Illinois. He served as an officer during the Black Hawk War whose soldiers remembered the "stern coarseness" of his leadership.^[2] He was an attorney for the state from 1834 to 1835, and was elected representative to the state house, serving from 1836 to 1838. Duirng this term Richardson served alongside Stephen Douglas and Abraham Lincoln.^[3]

In 1837 he supported Lincoln in making Springfield the capital of Illinois, after the charter for Vandalia expired.^[4] Richardson was a supporter of President Andrew Jackson against the Second Bank of the United States. At the state level he supported a bill that would make bank directors and stockholders responsible for redemption notes that citizens had with the state.^[5] When Governor Joseph Duncan defended the Bank, Richardson and other Democrats introduced a resolution calling such claims "contrary to the assertions of the patriot and statesmen, General Jackson."^[6]

He was narrowly elected to the state senate in 1838 by only seven votes which almost led to a duel between Richardson and his opponent's campaign managers.^[7] He served to 1842 deciding against reelection. Richardson returned to the house again from 1844 to 1846, briefly serving as speaker of the lower house during his last term. He was a presidential elector in 1844 for successful Democratic nominee James K. Polk.

When the Mexican-American War broke out, Richardson raised a company of volunteers who then chose him as their captain in the U.S. Army. Initially under John J. Hardin's command, Richardson's regiment was later placed under General Zachary Taylor and by the end of the war Richardson was promoted to Lieutenant-colonel.^[8] A strong defender of the war one of his first actions in congress was introducing an unsuccessful resolution calling the conflict "just and necessary".^[9] When his term of service expired in July 1847, he moved to Quincy, Illinois, and then was elected a U.S. congressman to the 30th Congress to fill Stephen A. Douglas's seat. He was then reelected to the 31st, 32nd, 33rd, and 34th Congresses for the same seat (1847 to 1856).