The boundary: after 1929, an Oliver tractor is an Iowa tractor

1929 – 1976

The merger line, at pointer size: On 1 April 1929 the Oliver Chilled Plow Works merged with the Hart-Parr Tractor Company of Charles City, Iowa, the Nichols & Shepard Company of Battle Creek, Michigan, and the American Seeding Machine Company of Richmond, Indiana, to form the Oliver Farm Equipment Company, with its corporate headquarters in Chicago. The Businesses record owns that course; what this section must fix is the geography that followed from it, because it governs every "Oliver tractor" a St. Joseph County farm ever bought. On Oliver Heritage's account, the merged company's plants remained at their existing locations — and the tractor plant among them was Hart-Parr's, at Charles City. South Bend's Factory No. 1 kept the implements. From 1930 forward, the Oliver tractor line — the 18-28 and 18-27 row crops, the 70, and every Oliver after — was built at Charles City, Iowa; TractorData's model records state the seat in so many words ("Built in Charles City, Iowa, USA").

The Hart-Parr inheritance, at pointer size: The tractor engineering South Bend merged into was itself an Indiana-age story told elsewhere: Charles Hart and Charles Parr formed their engine works at Madison, Wisconsin, moved to Charles City in 1900, and completed their first gasoline traction engine over the winter of 1901–02; the standard record credits Hart-Parr with introducing the word "tractor" itself for the machine. Hart left in 1917; Parr remained until his death in 1941. The Oliver Farm Equipment entry in the Businesses record carries the succession; here it is enough that the word on the merged company's tractors was coined at the Iowa works, not the Indiana one.

The crawler line, and the end: Oliver acquired the Cleveland Tractor Company — Cletrac — in 1944, the year the company became the Oliver Corporation; the crawlers continued at Cleveland, Ohio, crawler production moved to Charles City in 1962, after White Motor's purchase of Oliver on 1 November 1960, and all crawler production halted in 1965. White combined Oliver with Minneapolis-Moline into White Farm Equipment in 1969, headquartered at Oak Brook, Illinois. The last green Oliver tractor, a 2255, rolled off the Charles City line in 1976 — the company itself is dated defunct 13 February 1976 in the standard record — and in the mid-1970s Fiat-built tractors were marketed under the Oliver name (the Oliver 1465 among them): imports wearing the name, built in neither Iowa nor Indiana. No Oliver tractor of the merged era was built in South Bend; what South Bend built for those tractors is the next entry's subject.

Sources:

1. Oliver Heritage (oliverheritage.com), published company history — the plants remaining at their existing locations after the merger; the Cletrac acquisition (1944), the crawler move to Charles City (1962) and halt (1965); the Oliver Corporation name (1944); the last 2255 (1976).
2. TractorData, Oliver 70 and the Oliver model roster — "Built in Charles City, Iowa, USA"; the production line from the 18-28 of 1930.
3. Oliver Farm Equipment Company, the standard company record (Wikipedia, citing C. H. Wendel, Oliver Hart-Parr, 1993) — the merger of 1 April 1929 and its four parties; White's purchase of 1 November 1960; the company defunct 13 February 1976; Fiat tractors marketed under the Oliver name in the mid-1970s.
4. Businesses — the Oliver corporate course, owned there and pointed to here.