William Brown McKinley (September 5, 1856 – December 7, 1926) was an American banker and Republican politician who represented the state of Illinois in the United States House of Representatives for seven terms (1905–1913, 1915–1921) and in the United States Senate for one term from 1921 to 1926.

He also served as national campaign manager for President William Howard Taft's re-election bid in 1912, securing Taft's nomination by the Republican National Convention.

William Brown McKinley was born on September 5, 1856, near Petersburg, Illinois.

After attending the University of Illinois at Urbana-Champaign for two years, in around 1875 McKinley worked as a drug-store clerk in Springfield. He soon returned to Champaign to become a banker, specializing in farm mortgages.^[1] He entered politics in 1902, being elected a trustee of the University of Illinois. McKinley ran for the U.S. House of Representatives in 1904, winning his first of four consecutive terms. He lost re-election to the House in 1912.^[2] His re-election loss coincided with his service as national campaign manager for incumbent President William H. Taft, who also lost in 1912.^[3]

Voters in 1914 returned McKinley to the U.S. House,^[4] where he served from 1915 until 1921. In 1920, McKinley was elected to the U.S. Senate, taking office in 1921. In 1926, he ran for re-election and lost to Frank L. Smith (who ultimately was denied the seat by the Senate on the grounds of fraud and corruption in his campaign).^[5]

McKinley also was chief executive of the Illinois Traction System, an interurban electric railway. The McKinley Bridge between Venice, Illinois and St. Louis, Missouri was named for him. The McKinley Health Center at the University of Illinois at Urbana-Champaign is also named for him. McKinley died aged 70 in Martinsville, Indiana.

• List of United States Congress members who died in office (1900–49)