In 1986, CP sold the Guelph and Goderich Railway to a group of local investors who thought that they could develop Goderich’s port so that it wasn’t just originating salt. The railroad was soon filled out by adding a line between Guelph & Owen Sound and then, in 1992, a branch to Stratford (on the CN’s line to Goderich, which was in the process of being abandoned.)
Developing the port of Goderich never actually panned out (any sort of bulk reload facility would cost serious money with no guarantee of attracting traffic, and none of the shippers who used the lake were willing to commit to landing at the port without having facilities in place) but the railroad managed to retain enough salt traffic and carload freight from the branches to stay healthy.
Meanwhile, further to the southwest, a group of investors managed to grab most of the Michigan Central’s Canada Southern Railway when Conrail let it be known it was for sale or abandonment (most of because CN & CP were veeeery interested in the Michigan Central’s Detroit River tunnel, and the new owners of the Canada Southern were happy to let them have it in return for trackage rights instead of engaging in a ruinous bidding war for the entire property.)
CASO had been pretty thoroughly run down under Conrail’s watch, and the east end (from the Welland Canal to the Niagara River) was already scheduled to be transferred to CN, but fortuitously the east end of GTW’s line from Brantford to Fort Erie via Port Colbourne was also in the throes of being abandoned so it was purchased to redo the Buffalo<->Detroit bridge line that Conrail had just decided to throw away.
There was very little traffic on the line (and the handful of branches that had not already been closed) but a fairly dedicated marketing crew managed to preserve what little was left plus bring back a few big shippers, which made the line more than a little profitable.
In 1990, CN wanted to get rid of the remaining lines of the Niagara, St Catharines & Toronto, and the investors put down enough money to purchase them en masse to increase the traffic base of the railroad, and in 1995 Canada Southern (a) bought the Guelph & Goderich, then merged with the Ontario Radial Railway Company, which had just completed buying – and re-electifying! – the Lake Erie & Northern, which gave a connection between the CASO & the G&G instead of trackage rights on CN & CP (both of which were beginning to think that letting CASO go in return for the Detroit River tunnel was maybe not the best idea.
At this point the railway was renamed to the Ontario Southwestern, because it was no longer just a bridge line in the south.
OSW settled down to a comfortable existance, but 11 years after the merger one of the corporate backed investors bought out the rest and then revealed – by announcing a merger – that they were backed by the LT&L up in Québec, and so in 2007 the OSW stopped existing as an independent railway and became the LT&L’s Ontario subsidiary, connected to the rest of the PV&T system by the Delaware & Hudson (in Buffalo; the crossing at Niagara Falls had been out of service for a while as the city of Niagara Falls wanted to develop their downtown as a tourist attraction) via a circuitous route through southern New York.
In 2023, more route changes started to happen as part of the China Tunnel Railway project; the ex-GTW line from Fort Erie to Canfield Junction via Port Colborne was taken out of service, replaced by the D&H’s trackage rights west of Fort Erie (the old Welland branch, rerouted through the Townline tunnel on the NStC&T’s ex-Penn Central track) and a section of ex-Air Line from Welland to Canfield Junction.
The OSW (and the component radials of the ORRC) still maintain distinct identities because the Parsons Vale system had decided that it helped preserve local connections if the components of the system weren’t so obviously part of a distant faceless charitable trust (at least that’s the excuse; the TdM’s aggressive defence of their pre-merger identity had worn down the central office to the point where they started to appreciate that their engine servicing facilities weren’t an endless sea of blue and white.)