The OS&HU was formally reconstituted as the Northern Railway of Canada in 1858. While Simcoe County welcomed this new form of transportation, inevitably disputes arose from the reality and the perception of monopoly. The fight over "the Barrie Switch", a campaign for the construction of a spur from Allandale to downtown Barrie, (which was not accomplished until 1865) was arguably the bitterest of these.

In the meantime, by 1869, both Toronto and Simcoe County business and civic interests, agitated for an extension of the Northern Railway to Orillia, which resulted in the incorporation in late 1869 of the Toronto, Simcoe & Muskoka Junction Railway to build from Barrie to Orillia and beyond to a terminal on Lake Muskoka. The line to Orillia was completed in 1872, and opened to Muskoka Wharf in 1875.

Almost simultaneously, the Northern, which as a matter of policy was not in favour of branch line expansion, was pressured by the prospect of the Toronto, Grey & Bruce Railway (to Owen Sound) into the North Grey Railway that opened from Collingwood to Meaford in 1872.

All this activity had not escaped the business community of Hamilton, who in 1872 had chartered the Hamilton & North Western Railway to build through Simcoe County to connect with the forthcoming transcontinental railway. The Northern viewed this prospective competition with great concern, and endeavoured to stave it off with the concept of the South Simcoe Junction Railway, a line projected to branch off at King City in York County, and to serve the western portion of Simcoe County by way of Beeton, Alliston, Angus and Penetanguishene. Meanwhile a Simcoe County delegation put pressure on the Hamilton & North Western to build a branch from Beeton to Collingwood, and Simcoe County, fed up with the Northern monopoly and still smarting from such injuries as the Barrie Switch, voted its bonuses to the Hamilton railway. The Hamilton & North Western reached Barrie in 1877 with a terminus at Sophia and Bayfield Streets. The branch to Collingwood encountered engineering problems north of Creemore and did not reach Collingwood until early 1979, shortly before the announcement of its merger with the Northern Railway of Canada. 

For a few months Simcoe County basked in its newly-found competition and service to the inner reaches of the county, when the Northern and the Hamilton & North Western announced a joint operating agreement to form the Northern & North Western Railways. A storm of civic anger erupted as the reality sank in that the Hamilton & North Western had not ventured there for the exclusive purpose of giving its burghers competition with the Northern (although that is how it was sold for bonus purposes). The main reason for this merger was financial necessity arising from the ambition of both railways to make a connection at North Bay with the proposed transcontinental railway. After all, the "North Western" stood for Canada out West, not Simcoe County.

(For more information on the Hamilton & North Western and Northern & Northwestern Railways, please click here.)

Just before the Northern & North Western merger, Toronto business interests also incorporated the North Simcoe Railway "from a point on the Northern Railway" (Colwell) to Penetanguishene, built and opened in 1878. The North Simcoe Railway was constructed at the behest of the lumber interests in Flos Township, resulting in the incorporation and opening of the Flos Tramway in 1880. This spur ran from Elmvale to Hillsdale, south of Orr's Lake, and was acquired by the Northern & North Western Railways in 1882. Lumber operations are believed to have ceased in the 1890s, but the track was not lifted until 1917, a portion of it as late as 1927. In 1883 another lumber line came into being, the Medonte Tramway, built from Coldwater (off the Midland Railway, see above) south for about nine miles, also in the general direction of Hillsdale. Little is known about its disposition, but there appears to be agreement that it was lumbered out by about 1893.

While all this Toronto-Hamilton-axis activity was going on, Port Hope and Peterborough were busy with their own railway ambitions. The original 1846 charter of the Peterborough & Port Hope Railway became the 1854 Port Hope, Lindsay & Beaverton Railway that originally aimed for Lake Simcoe. When greater ambition beckoned, it then set its sights on Georgian Bay and changed its name in 1869 to the Midland Railway of Canada. Construction from Beaverton to Midland began in 1872, but bogged down. The line entered present-day Simcoe County at Gamebridge and was completed to Atherley in 1873, to Waubashene in 1875 and on to Midland in 1879. Peterborough interests then took control, and after acquisition of some smaller neighbouring lines in 1882, the Midland was leased to the Grand Trunk Railway in 1884, and acquired by the same in 1893.

From its original Portland - Chicago corridor, the Grand Trunk had gradually expanded in Ontario to the point of almost complete control within the province. With its acquisition of the Northern & North Western in 1888, and the Midland in 1893, Simcoe County had become part of a much larger monopoly by the turn of the 20th century.

The Canadian Pacific Railway had started to make inroads into Ontario in the early 1880s with its Ontario & Quebec Railway (which gave it access to Toronto from Montreal), and with its acquisitions of the Credit Valley and Toronto, Grey & Bruce Railways that had secured footholds to St. Thomas and to Owen Sound respectively. At the turn of the 20th century, the CPR had therefore loosened the grip of the GTR's stranglehold, and by 1906 it was ready to build its own connection between Toronto and its transcontinental line. The CPR's route through Simcoe County was very similar in parts to that envisioned by the Hamilton & North Western Railway in its original 1873 prospectus, except that Alliston was the only community of any size to have a station close to its main street, with the result that the major reliance for local traffic remained with the Grand Trunk.

The decade prior to World War I was one of feverish transcontinental railway construction in the anticipation of booming prairie settlement. To compete with the Grand Trunk and the CPR, MacKenzie and Mann's shiny new Canadian Northern Railway needed Ontario links to its transcontinental plan, and this came to pass as what was renamed in 1906 as the Canadian Northern Ontario Railway's line between Toronto and Sudbury, originally chartered in 1895, and commonly referred to as the James Bay Railway. From the south, it began service through present day Simcoe County in 1908 at Gamebridge, with stations at Brechin, Udney, Washago and Sparrow Lake.

Meanwhile, with an eye to the grain traffic on the Great Lakes, the CPR sponsored the Georgian Bay & Seaboard Railway, also known as the CPR's Port McNicoll branch, to avoid the delays and the additional distance of shipping to Montreal through Toronto. This line was opened in 1912 by building from the newly deepened Victoria Harbour, creating a community known as Port McNicoll, with stations at Tay, Fesserton, Coldwater, Coldwater Junction (intersecting its newly-built Sudbury line at a point called Medonte), then veering by Uhthoff and Tafton across to Orillia, passing across the Narrows to Atherley, then on to Uptergrove, and via Brechin across country to Lindsay, and thence to Bethany Junction on the CPR's Havelock line. The very lightly used passenger service was discontinued in 1932, and this road was abandoned from Orillia to Bethany Junction in 1937. The last regular traffic across the curved landmark-Hog Bay trestle between Port McNicoll and Medonte was in the mid-1960s.

The only addition that the Grand Trunk Railway made in Simcoe County was a connection between the former North Simcoe (its Penetang branch) and Midland (its Belleville and Midland branch) railways, from a point three miles north of Elmvale, known as Birch, with a station at Wyebridge, connecting with the Midland line between its stations at Victoria Harbour and Tiffin at a point near Old Fort. It was opened in 1911.