This list is under construction as I finish uploading observations from 2020.

Here are the 100 most common species observed in Ontario that I personally had not observed prior to the year 2021.

Filters used:
Display species
Verifiable, research grade
Observed in Ontario
Unobserved by mws
At species rank
Uploaded before January 1st 2021

https://www.inaturalist.org/observations?created_d2=2020-12-31&d2=2020-12-31&place_id=6883&quality_grade=research&rank=species&subview=grid&unobserved_by_user_id=mws&view=species