Anton LaVey, founder of the Church of Satan, claimed to have been born on the spot where the Hancock Building now stands. If true, it would probably the only thing he ever said that wasn't straight up nonsense.
LaVey was always far more of a showman than a religious figure. At various times he claimed to have been a church organist, a lion tamer, a gypsy, and any number of other things that turned out to have no basis in fact. He freely and cheerfully admitted that he lied like crazy - he was said to claim that he'd "be full of shit if I didn't keep my mouth shut and my bowels open."
So, what of the claim that he was born where the Hancock building now stands? Records indicate that he was born in Chicago in April, 1930, but I can't find anything that states the location of his birth (short of trying to get ahold of a birth certificate, which ain't free).
However, we can dig up a few things about the plot of land where the Hancock stands. In 1928, it was occupied by The Casino Club - the club is still there, but in a slightly different location, having moved to the northeast corner of the block when the land of the original site (on the same block) was sold out from under them to residential real estate company. It now stands in the shadow of the Hancock, the only other structure on the block. As of 1928, it was THE place for the high society set to gather. Being a black building with an unlisted phone number and no sign on the door, I imagine it still is, though the exploits of the club are no longer a regular feature of the newspaper (as they were back in the 1920s).
What exactly that company built on the spot I haven't yet found - I'm guessing it would have been very upscale residential places, probably with some retail shops on the first floor. I certainly don't see any evidence that a hospital was built on the site. As of 1965, when construction on the Hancock began, the site seems to have been a parking lot (on one what one guy called the most valuable patch of land in the midwest).
So, I can't find anything that would definitively refute the story about LaVey, but certainly nothing to back it up. Like most of LaVey's tales, about the best we can probably say is that it makes a pretty good story, going right along with the stories of Cap Streeter putting a curse on the neighborhood - as I've said before, if Streeter DID put a curse on Streeterville (which also seems to be a myth), he must have really sucked at cursing things. If you have any documents that show his place of birth (beyond just the county), send 'em along, will ya? I could always order some records, but frankly I don't think it's worth the price.