The Blue Book ledger, at county frame

1947 — 1969, the project's whole span

The sweep: Mishawaka's one line can be enumerated exactly because the Air Force indexed its own cases. In the work behind this history's South Bend file — repeated here because the ledger is the county's, not one city's — the Air Force's published yearly indexes for every year of the project, 1947 through 1969, in both digitized copies of each, were searched for South Bend, Mishawaka, Notre Dame and the witness names the record supplies, and every Indiana location line in every year was read. The yield for St. Joseph County is four cases, and they are the whole of it: 13 October 1948, South Bend, evaluated "Other (DEBRIS IN AIR)"; 8 May 1952, Mishawaka, "Insufficient Data"; 23 July 1952, South Bend, "Unidentified"; and January 1957, South Bend, "Insufficient Data." No case is indexed under Notre Dame, the unincorporated community that holds the universities; none under Osceola, Walkerton, New Carlisle or any other county place. The Air Force's published list of official "Unknowns" was likewise swept in full: Indiana holds seven of its entries — Indianapolis twice (29 and 31 July 1948), Kokomo (8 April 1950), Terre Haute twice (9 October 1951 and 26 June 1952), Rockville (22 July 1952) — and South Bend once, the pilot's case of 23 July 1952. Mishawaka's name appears on no such list; its county standing is one case in four, closed as too thin to judge, beside the one case in four the Air Force never explained. The other three cases stand whole in the South Bend build's Aliens section, where their city keeps them; they are boundary-printed here, in this ledger, at the size the county frame requires, and not absorbed into Mishawaka's count.

The limit, stated: The enumeration is an enumeration of the indexes, made on digitized text layers of scanned documents, and it carries that limit openly; the reading of every Indiana line, and not name-matching alone, is the guard against a garbled line escaping the net. The case files themselves sit at the National Archives in chronological order on microfilm T-1206 — and, as the 1952 entry records, no file under Mishawaka's name stands in the Archives' catalogued folder titles at all. What the ledger settles is the county's official footprint: four cases in twenty-two years, one of them Mishawaka's — a small city's small share of a national file of 12,618.

Sources:

1. U.S. Air Force, Project Blue Book yearly indexes, 1947–1969 (redacted and unredacted digitized copies, archive.org, ProjectBlueBookIndexes, from the National Archives records) — searched in full; the county's four lines as quoted in this history's case entries.
2. U.S. Air Force, cases officially listed as "Unknown" (published list, as reproduced at nicap.org/bluebook/bluelist.htm; 564 entries of the 701 the Air Force claimed) — swept in full; Indiana's seven entries as listed.