Elections Ontario says preliminary results show 566,845 voters have cast their ballots in advance polls ahead of the provincial election, to be held on Thursday.
Advance polls for this year's election were open for a week ending last Friday.
In the 2011 election, 603,785 people voted in the advance polls, which were open for 10 days.
Elections Ontario says the daily vote count this year represents a 25 per cent increase from 2011.
Opinion polls conducted during the campaign have consistently shown a high number of undecided voters.
The 2011 election saw the lowest turnout in the province's history, with only 49 per cent of voters casting a ballot.