Population of Port Arthur and Fort William in 1951 was 66,108. Including the surrounding townships, the population of the area was probably somewhere around 72,000.
Port Arthur and Fort William merged in 1970 to form Thunder Bay, and the geographic townships of McIntyre (part of Shuniah) and Neebing (part of Neebing) were annexed by Thunder Bay at the same time to form the modern city limits.
Shuniah was formed in 1871, comprising the townships of McTavish, MacGregor, McIntyre, Neebing, Blake, Crooks and Pardee. The latter four split from Shuniah in 1882 to form the municipality of Neebing. Port Arthur split from Shuniah in 1884, Fort William split from Neebing in 1892. The other townships were created at later dates.
I don't know exactly why the dividing line between McIntyre and Oliver is further west, but I think it might have something to do with the creation of Port Arthur.