The Medicaid program is the third largest source of health insurance in the United States - after employer-based coverage & Medicare. Medicaid covered 12 percent of the total U.S. population (or 40.6 million people) in 1998, compared to 9.1 percent in 1978. The number of persons served through Medicaid remained relatively constant from 1977 to 1989. However, eligibility expansions mandated by Congress in the late 1980s led to significant increases from 23.5 million covered in 1989 to 36.3 million covered in 1995.