There were 550,000 about 10 years ago, but two things happened. First, immigration played a role, but in addition, Ontario adopted what may be a unique approach: the province adopted an inclusive definition of the francophonie.
While keeping in mind section 23 of the Canadian Charter of Rights and Freedoms, which concerns the right to schooling in the language of the minority, imagine the case of a francophone immigrant. Under this article, in Ontario as in the other provinces with the exception of Quebec, if a francophone is not a rights holder under the Charter, he or she must apply to an admissions committee to be allowed to attend a French school. Just imagine that, if you will. In Ontario 10 years ago, if a French person from France arrived in Ontario and wanted to go to a French school, he had to apply to an admissions committee.
What Ontario did to make that approach more flexible was to make any person who spoke French and arrived in Ontario a person who had the right to schooling in French, even if that was not their mother tongue. That is being done in Ontario, but let's be clear, it is not the case everywhere in Canada.
By adopting that inclusive definition in 2003, I believe, 50,000 more immigrants were included as francophones, so that there are now 611,500.