Disability categories (according to NY State)
This is the actual text of the N.Y. law regarding definitions of various disabilities. Again, citing this is pretty tricky - I think this is correct:
Important: Make sure to replace "X" with the number appropriate to the disability. For example, traumatic brain injury would be N.Y. Comp. Codes R. & Regs. tit. 8, § 200.1(zz)(12).
Government Information About Disabilities
This site seems to be one of the more authoritative sources for descriptions of disabilities in the U.S.
Even though this isn't a government site, most of the content on this site was originally on the website of the National Dissemination Center for Children with Disabilities (NICHCY), a project funded by the U.S. Department of Education. However, as of 2014, NICHCY lost its funding. Much of the content on the NICHCY website was migrated to this site.
Most government agencies still refer to the CPIR site.