In a message released by Buckingham Palace today, the Queen said she was moved by the messages of support sent to her and the Duke of Edinburgh during her Diamond Jubilee year.
She also spoke of her hope for united families and communities, and a spirit of "neighbourliness".
"Today, as I mark 60 years as your Queen, I am writing to thank you for the wonderful support and encouragement that you have given to me and Prince Philip over these years and to tell you how deeply moved we have been to receive so many kind messages about the Diamond Jubilee," she said.
"In this special year, as I dedicate myself anew to your service, I hope we will be reminded of the power of togetherness and the convening strength of family, friendship and good neighbourliness, examples of which I have been fortunate to see throughout my reign and which my family and I look forward to seeing in many forms as we travel throughout the United Kingdom and the wider Commonwealth.
"I hope also that this Jubilee year will be a time to give thanks for the great advances that have been made since 1952 and to look forward to the future with clear head and warm heart as we join together in our celebrations.
"I send my sincere good wishes to you all."
Accession Day is marked each year on February 6, the day in 1952 that the 25-year-old Elizabeth's father, George VI, died and she became Britain's Queen.
David Cameron, her 12th prime minister, paid tribute to the 85-year-old monarch's "magnificent service".
"With experience, dignity and quiet authority she has guided and united our nation and the Commonwealth over six varied decades," he said.
Two official photographs were released by Buckingham Palace to mark the day. In London, a 41-gun salute will be held in Hyde Park and a 62-gun salute at the Tower of London.
In Edinburgh, a 21-gun Royal Salute was held at Edinburgh Castle at noon.
The Queen was today visiting King's Lynn Town Hall and an infant and nursery school in nearby Dersingham.
Larger-scale events will be held later in the year to celebrate the Queen's Diamond Jubilee. Churches across the country are planning to light beacons and hold parties.