Is that across all universities? Because I would guess that, for example, University of Illinois gets a much larger portion of its funding from government sources than University of Chicago (which would be one of those well-endowed universities which, incidentally, just cut tuition to zero for undergrads from families making less than $250K).
University of Illinois is also a public school. University of Chicago is private, as is MIT.
This study estimates that government spending is 40% of public university revenue, ~10% for private schools. https://nces.ed.gov/programs/coe/indicator/cud/postsecondary...