William Alexander Richardson (January 16, 1811 – December 27, 1875) was a prominent Illinois Democratic politician before and during the American Civil War.

During the American Civil War, he switched from supporting the conflict to join the Copperhead wing of the Democratic party and bitterly criticize President Abraham Lincoln.

[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.

[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.

Afterword, when confronted in Illinois about the unpopular Fugitive Slave Act, Richardson said that while he personally opposed the law he supported it in order to ensure the admission of California.

[11] During the crisis Richardson lamented the rise of secessionist sentiment: There is a bad state of things here, and, as little as it is thought about, I fear this Union is in danger...

His initial bill introduced on February 2, 1853, contained no mention of slavery and was supported by representatives Willard P. Hall and Joshua Giddings.

[21] Richardson's stance on the Wilmot Proviso undermined his position with Southern Democrats and three South Carolina reps abandoned him on the next ballot which was the 108th.

[22] Under pressure from President Franklin Pierce for a resolution to the stalemate in the house, Democrats replaced Richardson with James Lawrence Orr.

He resigned in August 1856 to run for Governor of Illinois, narrowly losing to fellow representative, and first nominee of the newly established Republican Party, William H. Bissell.

In 1863, he was elected to fill Stephen Douglas's old seat in the United States Senate, defeating incumbent Republican Orville Browning.