I swear, it's amazing what you can learn if you just pay attention. When I look at Census records, I've always focused on the names and ages. I never before noticed that the 1850 and 1860 Census forms have a column labeled "Whether deaf and dumb, blind, insane, idiotic, pauper or convict."
The 1840 Census asked "The number of White persons who were insane and idiots (at public and private charge)
The 1890 Census asked "Is the person defective of mind, sight, hearing, or speech? Is the person crippled, maimed, or deformed? Is the person a prisoner, convict, homeless child, or pauper?
Amazing what you can learn when you focus on a particular issue. So, for 50 years the national government kept track of the numbers of insane, blind, deaf, and mentally defective people in the country.