http://en.wikipedia.org/wiki/Social_Insurance_Number
The first digit of a SIN indicates the province in which it was registered:
1: Atlantic Provinces: Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland and Labrador
2: Quebec
3: Quebec
4: Ontario (including overseas forces)
5: Ontario
6: Prairie Provinces (Manitoba, Saskatchewan, and Alberta), Northwest Territories, and Nunavut
7: Pacific Region (British Columbia and Yukon)
8: Not used
9: Temporary resident
0: Not used (Canada Revenue may assign fictitious SIN numbers beginning with zero to taxpayers which do not have SINs)
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Note: While the first digit usually identifies the location of registration, the government has found it necessary in the past to supply certain regions with SIN numbers assigned to other regions.
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