One of the reference databases SLPL subscribes to is Fold3.com. Fold3.com concentrates on military records, although it also provides various non-military records.
Fold3.com provides access to a hybrid category of sorts: the U.S. Air Force Project Blue Book Investigations. I call it a hybrid category in that military personnel were investigating incidents reported sometimes by service members but more often by civilians.
Project Blue Book was the third in a series of studies of possible UFO activity (the first two were Project Sign and Project Grudge). Project Blue Book was by far the lengthiest and most thorough study: during its 17 years of existence (1952-1969), it generated 12,618 reports on suspected sightings. That’s approximately 750 such sightings per year on average!
Sighting investigations can include:
Cover sheet or record card
UFO Incident Checklist
Description of Incident
Correspondence to/from observer(s)
Photos, drawings, or diagrams (don’t expect many photos)
Official report with conclusion (explained/unexplained)
Reported sightings came from all over the world (although a majority are U.S. sightings). You can browse through all the Project Blue Book reports, if desired, or you can do an Advanced Search. I searched using these qualifiers:
Place name: Missouri
Year range: 1952-1969
This search filtered for Project Blue Book results returned 1,771 hits, including some St. Louis area sightings (Kirkwood, Festus, Overland, and Florissant among them).
Some good news for you: holders of a valid SLPL library card can search this database from home! To get started, go here.