The Pontiac, Oxford and Port Austin Railroad ran north from Pontiac to Caseville on Lake Huron, in the thumb of Michigan. Originally incorporated as the Oxford and Port Austin Railroad in 1879, with a subsequent name change to the PO&PA in 1880, the railroad was completed in 1883. As indicated in its name, the PO&PA was originally destined for Port Austin (also on Lake Huron); however, widespread fires at the time burned a considerable portion of the lumber industry in the area around Port Austin, so the destination was moved to Caseville instead.
In total, the route was right at 100 miles long (the official measurement submitted in its valuation to the ICC was 99.894 miles). Here is a rough timetable of the PO&PA:
By 1889, with insufficient passenger revenue due to the sparsely-populated region through which it traveled, the PO&PA filed for bankruptcy, and the line emerged as the Pontiac, Oxford & Northern Railroad. Freight was primarily driven by local farm production, namely wheat, beans and sugar beets.
The railroad came under the control of the Grand Trunk Western in 1909, by which this line was called the Cass City Subdivision. During this time, the GTW built a branch line (also abandoned) from Cass City northeast to a connection with the Pere Marquette Railroad in Bad Axe.
The GTW originally filed for abandonment of the line in 1974, but formal abandonment came in two stages: between Kings Mill and Caseville in 1984, with the remainder of the line in the 1990s. There is a small section of the line north out of Pontiac that is still in use to serve the General Motors plant at Lake Orion.
Today, some of the line serves as the Polly Ann rail-trail. Additionally, some of the original rail and a monument in the Caseville municipal park pay tribute.