The 1992 NIDRR Report:

A comprehensive analysis to determine how many Americans have disabilities that do limit activities was prepared for the U.S. Dept. of Education (DOE) by the University of California (UCSF)'s Institute for Health and Aging. A report on their findings was published in June, 1992 by the DOE's National Institute on Disability and Rehabilitation Research (NIDRR):

Here's that report: How Many Americans Have a Disability?

Based on 1990 data, the Institute for Health and Aging estimated that the number of Americans with disabilities "severe enough to limit their daily activities" was:

“36.1 million in 1990, or 14.5 percent of the 246 million people residing in the U.S.” [at that time]

Which means that in 1990, ONE out of every SEVEN people living in the United States had a “severe” disability.

But that study was completed over twenty-one years ago, and the numbers have grown considerably since then.