Honestly, there's no real way to tell exactly where the laser hit. Most of the following information is constituted on a basis of visual judgement.
Given its trajectory, the laser would most likely have hit the Earth somewhere near Algonquin Provincial Park in Ontario, Canada. Once again, this is merely an approximation. The explosion has been confirmed by canon sources to span around an area of 350 miles, or about 550 kilometers (a little bit past Detroit or Cleveland).
350 miles from Algonquin Provincial park is just enough to reach Toronto. Judging by the metric system, the distance between Toronto and Algonquin park is roughly 457km. Considering that, the great lakes take up about 100km worth of space between Canada and the states. Therefore, the total span of the explosion reaches a total span of 350 miles.