Ontario Island was a glacial feature as lobes of the Laurentide Glaciation receded from southern Ontario. [1] [2] The glaciation started to retreat approximately 20,000 years ago. As it retreated its southern edge was ringed by a series of proglacial lakes. The relatively high ground, west of the Niagara Escarpment formed a large island in these lakes.
The first part of Ontario to become ice free was the high ground west of the Niagara Escarpment in south-central Ontario, a region geologists call Ontario Island.
The higher ground to the north of here, sometimes referred to as "Ontario Island," because it was surrounded by shrinking ice lobes and growing glacial lakes, tended to deglaciate first.