Higher education, as we know it, started in the US in 1636 with the establishment of Harvard College, which would be named Harvard University about 150 years later. For the next 300 years, higher education would have a slow-but-steady growth. After World War II and the establishment of the Servicemen's Readjustment Act of 1944 (the GI Bill), higher ed exploded in the US. And with the boomers, it "massified" even more in the 60s and 70s. Only over the last decade have we seen declines in enrollment.
The greatest growth in higher education enrollment occured between 1960 and 1970, with a doubling of students (107 percent increase) during the decade. This was buoyed by the establishment of California's "Master Plan" of higher education, which created the three tiers of the University of California, California State University, and the California Community College systems.
Today, for the first time in 150 years, enrollment is regressing. Between 2010 and 2020, enrollment declined nine percent from 21 million to 19 million. These declines are expected to continue for the next foreseeable future.
SOURCE: Snyder, T.D. (1993). 120 years of American education: a statistical portrait. National Center for Education Statistics, Washington, DC: U.S. Government Printing Office; Digest of Education Statistics 2023, Table 317.10: https://tinyurl.com/e77c9v78.