There are many species of tarantulas, the venom differs from species to species. Several of the larger ones are sold as pets by pet shops.
I remember doing fieldwork in Limestone County, Texas, one year when they were at top of a cycle. They were everywhere. The worst problem with the bite, at least with most species, is the chance of infection.
There are many tales of particularly venomous types, but I haven't looked into the facts. Those in North America are not dangerous to most people. They seldom bite unless provoked.