The 100th United States Congress was a meeting of the legislative branch of the United States federal government, composed of the United States Senate and the United States House of Representatives. It met in Washington, D.C., from January 3, 1987, to January 3, 1989, during the last two years of Ronald Reagan's presidency. The apportionment of seats in the House of Representatives was based on the 1980 United States census.

John Cornelius Stennis was an American politician who served as a U.S. senator from the state of Mississippi. He was a Democrat who served in the Senate for over 41 years, becoming its most senior member for his last eight years. He retired from the Senate in 1989, and is, to date, the last Democrat to have been a U.S. senator from Mississippi. Furthermore, at the time of his retirement, Stennis was the last senator to have served during the presidency of Harry S. Truman.