William Allen Cullop (born March 28, 1853) was an American politician who represented the state of Indiana in the United States House of Representatives in the early twentieth century. A member of the Democratic Party, he served as the U.S. Representative for Indiana’s 2nd Congressional District. His tenure in Congress began on March 15, 1909, and concluded on March 3, 1917, spanning four terms in the House.

During his time in office, Cullop served as a Representative from Indiana at the federal level, participating in the legislative work of the House of Representatives as a historical member of Congress. Although specific committee assignments, legislative initiatives, or additional offices are not recorded in the available metadata, his eight years in Congress place him among the Democratic lawmakers who represented Indiana during that period. After leaving office in 1917, he held the status of a former member of Congress.