The 96-year-old head of state passed away at Balmoral in Scotland.
She visited Guernsey six times during her 70-year reign – most recently for Liberation Day in 2005.
Her official role was as the Duke of Normandy to the Channel Islands.
The Crown now passes to her son and heir, who is now King Charles III.
The King and The Queen Consort remained at Balmoral last night and are set to return to London today.
Tributes have started to come in locally.
Lt-Governor Richard Cripwell served the Queen in the army for more than 40 years, before becoming the Queen’s personal representative in the Bailiwick.
‘It was my most sad and solemn duty to receive official notification of the passing of Her Majesty and to convey it to others in the Bailiwick,’ he said last night.
‘Even in this time of great sadness, I know that everyone in the Bailiwick will always remember Her Majesty’s exceptional devotion to her people, her extraordinary service to those she represented and her love of these islands.’
King Charles issued a statement that everyone throughout the Commonwealth was mourning her passing.
‘During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which the Queen was so widely held.’
A period of national mourning has now commenced, which will continue until the end of the day of the state funeral.
There will be formal opportunities for members of the public in Guernsey to express their sadness and their condolences and there will be an official island thanksgiving service in the coming days.
An official condolence message has been sent on behalf of the people of Guernsey by the Lt-Governor, in liaison with the Bailiff and the Chief Minister.
It reads: ‘We, the Lieutenant-Governor and the Bailiff of Guernsey, the Deputy Bailiff, the Royal Court and the States of Guernsey, the President and the States of Alderney, the Seigneur and the Chief Pleas of Sark, and all the people of this Bailiwick with humble duty beg leave to offer to His Majesty The King and His family our respectful and sincerest sympathy on the death of Her Majesty Queen Elizabeth II, whose long and loyal reign stands as an inspiration to us all.
'Her Majesty will always be remembered with great affection across our islands, which she visited on six memorable occasions.’
Arrangements are being made for special meetings of the States of Deliberation and for other ceremonies to mark the passing of Her Majesty.
This will include gun salutes from Castle Cornet.
A full list of events related to the period of National Mourning will be made available over the coming days at gov.gg/monarch