She turns 80 on Friday. The queen expressed "thanks for our health and happiness" in a toast to 99 "birthday twins" invited to Buckingham Palace for a lunch to mark their common birth date of April 21, 1926.
The event, at the official London residence of Europe's longest-serving monarch, was like a fairytale to some.
"I nearly died when I found out I was going to the birthday lunch," Doreen O'Leery of Oswestry in west-central England said as she sipped a sherry.
The lunch, attended by the queen's husband Prince Philip, was among scores of events planned over the coming weeks to celebrate her birthday and the symbolic role she has played since the death of her father in February 1952.
As well as head of state, she is head of the Commonwealth, the British armed forces and the Church of England.
While her real birthday is April 21, Queen Elizabeth also enjoys an official birthday, this year on June 17, when the fickle English weather is deemed more favorable for outdoor festivities.
"On this special occasion I believe we can and should count our blessings," the queen told her guests.
"I doubt whether any of us would say the last 80 years has been plain sailing, but we can give thanks for our health and happiness, the support we receive from our families and friends, some wonderful memories and the excitement that each new day brings.
"Thank you for coming today and I hope all those of you who are my exact twins will make the most of our special day on Friday," she said.
Politicians pay tribute
Mr Blair told parliament that Queen Elizabeth had reigned with "extraordinary grace and dedication" and had been a "truly remarkable source of constancy and of strength."
She was one of the most "respected people of our times" and her "sense of duty and service" had a "profound impact on our country, the Commonwealth and the world," Mr Blair said.
David Cameron, leader of the main opposition Conservatives, said "she has been a rock of stability, calm and good sense in a period of the most turbulent change."
He recalled how her lifetime has witnessed the dismantling of the British empire, Britain's joining the European Community, the ending of the Cold War and the new millennium.
Reflecting the personal nature of her 80th birthday, Queen Elizabeth, who appears in excellent health, will spend much of this Friday privately with her family.