Where was Sleepaway Camp filmed?
1983 film by Robert Hiltzik
Sleepaway Camp (1983) was filmed in Washington County, Warren County, Glens Falls and Argyle, 4 places named in its Wikipedia article, in the United States. Wikidata records no filming location for it at all, so the article is the only recorded source. Each place says where its claim comes from.
Part of the Sleepaway Camp film series
Places per Wikipedia's article
The Wikipedia article names 4 places. Each links to the sentence that says so.

