In many (if not all) jurisdictions in the United States anyway, one may not simply visit prisoners. One must be on a list of approved visitors of specific inmates. The government simply will not allow any Tom, Dick, or Harry to walk in off the street and visit with the prisoners.
Some church organizations are allowed to visit with some prisoners, but these organizations also have to be pre-approved.
I don't see the possibility of just "visiting" the imprisoned today.