There have been many different newspapers published in Toronto over the years. For more information, see: Gilchrist, Brian. Inventory of Ontario Newspapers 1793-1986. (Toronto: Micromedia, 1987), and Firth, Edith G. Early Toronto Newspapers, 1793-1867: A Catalogue of Newspapers Published in the Town of York and the City of Toronto from the Beginning to Confederation. (Toronto: Toronto Public Library, 1961).
The best collection of Toronto newspapers—original and on microfilm—is at the Toronto Reference Library.
The Archives of Ontario also has an extensive collection of Ontario newspapers, including Toronto. Consult the Newspapers finding aids 212 and L23.
Library and Archives Canada also has a collection. Consult the list of microfilmed Toronto newspapers.
Two major Toronto newspapers have been digitized and are searchable for a fee: the Toronto Star, and the Globe and Mail. Toronto residents can access them for free through the Toronto Public Library. You can find great tips for searching in the Library’s blog. Many other public libraries and university libraries provide free on-site and remote access to these digital resources for their patrons and students.
The Toronto Telegram, another major Toronto newspaper that ran from 1876 – 1971, has not been digitized. It is available on microfilm at Toronto Reference Library and North York Central Library. This paper’s archives are held at York University Archives. The archives has digitized a selection of Telegram photographs.
OurOntario Newspapers, hosted by OurDigitalWorld, is a collection of free newspaper resources including indexes, clippings and full digitized issues. There are not many Toronto papers at present, but there are several from surrounding municipalities that may have picked up Toronto news. Since all papers can be searched at once, it is well worth a look.
A number of other Toronto newspapers have been digitized by Google News. It is important to note that they may not be searchable and you should expect to browse the images page by page. Unfortunately, some newspapers in this collection are poorly labelled and unrelated mastheads have been grouped together. Be cautious that you are looking at the correct newspaper. The two guides mentioned below will be very helpful.
Kenneth R. Marks maintains a wonderful site devoted providing links to online North American newspapers: The Ancestor Hunt.
Bowling Green State University (Kentucky) also has a terrific collection of links to Ontario Historical Newspapers Online.