My source was a map posted to Reddit in July 2024. However after doing more research, Wikipedia reports it is now actually 16 states.

Emphasis mine:

February 2024: the Attorney General of the state of Texas sued Aylo/Pornhub for allegedly not obeying the state’s legal age verification law.[141][142][143] As of March 2024, Pornhub and other Aylo-owned websites have blocked access in Texas, due to the adoption of an age verification law which usually mandates age verification through the use of an identity document. In states where Pornhub is blocked, which also include Alabama, Arkansas, Louisiana, Mississippi, Montana, North Carolina, Utah, Virginia, Florida, Nebraska, Indiana, Kansas, Idaho, Kentucky, and Oklahoma; a message is displayed featuring pornstar Cherie DeVille criticizing such laws.[