The One Hundredth 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 Twentieth Census of the United States in 1980. Both chambers had a Democratic majority.