As of July 1, 2016, over 80 million Americans, nearly a quarter of the population, was enrolled in Medicaid. [0] (Because someone qualified for other means-tested assistance will almost always also qualify for Medicaid, that's a pretty good rough estimate, though still a lower bound, for the total aid-receiving population at that point in time.)
[0] https://data.medicaid.gov/widgets/x3sw-xby3