The S.D. Perry novels put Raccoon City in Pennsylvania.
These books aren't canon but there was something interesting I read the other day. During an interview, she was asked what the reasoning was behind putting the city in Pennsylvania and she said she thinks it was her editor's idea who might have gotten it from Capcom.
If this did come from Capcom, then either they just threw out a state without much thought or regard for the novels (in the interview it came of as Capcom didn't really much care for the books and didn't provide her much direction) or they always had the idea that the city would be in or around that area.
That's a good bit of info on why PennsylvaniaIt may have been because at the time, Capcom was considering Pennsylvania because of its history with zombie films and George Romero. Romero also placed RC in Pennsylvania for his script, and may have been inspired by Evans City when writing.