There have been several stages in the history of Canadian independence.

Canada became a self-governing dominion within the British empire on [1 July 1867][1] when the [British North America Act][2] was passed by the UK Parliament.

The [Statute of Westminster][3], passed by the UK Parliament in 1931, acknowledged Canada as co-equal with the United Kingdom within the British Commonwealth.

Canada obtained full autonomy when the UK Parliament passed the [Canada Act 1982][4] in 1982. This granted full sovereignty to Canada, and so marks the date at which Canada became truly independent.

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As a side note, and as noted in the comments below, the [Queen's role as monarch of Canada][5] is entirely separate from her role as the British monarch. She is Queen of the United Kingdom, and also, Queen of Canada by an act of the Canadian Parliament ([*The Royal Style and Titles Act*][6]).

The fact that the Queen is head of state of both the UK and Canada (and also in 15 other Commonwealth nations) does not effect Canada's sovereignty as an independent country at all.


  [1]: http://www.history.com/this-day-in-history/canadian-independence-day
  [2]: https://en.wikipedia.org/wiki/Constitution_Act,_1867
  [3]: https://en.wikipedia.org/wiki/Statute_of_Westminster_1931
  [4]: https://en.wikipedia.org/wiki/Canada_Act_1982
  [5]: https://www.webcitation.org/5o4XQi18u?url=http://www2.parl.gc.ca/Sites/LOP/Infoparl/27/2/27n2_04e_trepanier.pdf
  [6]: http://laws.justice.gc.ca/eng/acts/R-12/page-1.html