The site went live today, allowing gamblers to play casino-style games including blackjack, baccarat, poker, roulette and slots.
People can also purchase lottery tickets on the new OLG site.
The lottery agency says Ontarians currently spend up to $500,000 a year gambling on grey market online sites that are not regulated in the province.
People must register to use the new site and establish mandatory weekly maximums for the amount they wish to gamble, but can take the money directly from bank accounts or use their credit cards.
British Columbia, Manitoba, Quebec and all the Atlantic provinces already offer online gambling.
(The Canadian Press) 11:47ET 08-01-15