so i asked my dad about stuff in the movie, and...
the scene in the mourge was at seaview hospital which was a tuberculousis hospital in the 1920's. it was genuinely creepy, according to my father who worked on the movie.
to get the morgue room ready, they had to get many bottles of tuberculosis lung samples out of the room. since there were so many deaths, there were actual underground tunnels connecting all of the wards to the mourge, and he's pretty sure another scene was actually shot in the tunnels.
the amusment park scene was taped at south beach amusement park, which actually closed recently. an interesting tidbit is that they needed to re-shoot a scene there, and they used one of the cameraman's 7 year old son. they wanted him in a close-up with cotton candy, but since there wasn't any cotton candy, they put pink fiberglass insulation in a big paper cone. his father was horrified.
at the time, tom hanks was really impressed with the actors, because he was still a nobody. my dad remembers driving to the staten island ferry and overhearing him talk to some of the leads about pointers for auditions and such. the lead male apparently had had some modeling job on an army recruitment poster, and tom hanks was impressed with the man's "success".
if there's anything else you guys would like to know, message me on here!