Scroll through the gallery above to relive the Queen's many visits to the county.
The Queen celebrates her 91st birthday today and is expected to spend the anniversary privately.
After her 90th birthday last year, which saw national festivities held in her honour, the 2017 milestone will seem more subdued.
But royal gun salutes will still echo across the capital later, fired by the King's Troop Royal Horse Artillery and the Honourable Artillery Company.
Princess Elizabeth Alexandra Mary was born at 2.40am on April 21 1926, the first child of the then Duke and Duchess of York, at 17 Bruton Street, the Mayfair home of her mother's parents, the Earl and Countess of Strathmore.
With the passing years have come milestones for the Queen.
She became Britain's longest-reigning monarch, passing her great-great grandmother Queen Victoria's record, in September 2015.
And with the death of 88-year-old King Bhumibol Adulyadej of Thailand last autumn, the Queen is now the world's longest reigning living monarch.
Earlier this year on February 6, the date she became Queen in 1952, she achieved another milestone, becoming the first British sovereign to reach their Sapphire Jubilee, a reign lasting 65 years.
The Queen is today thought to be at Windsor Castle, where she traditionally spends a month-long residence, known as Easter Court.
In Hyde Park, London, at midday, 41 volleys in honour of her birthday will be fired by the King's Troop Royal Horse Artillery.
Then an hour later the Honourable Artillery Company will fire a 62-gun salute at the Tower of London - an extra 21 for the City of London.
The Queen traditionally has two birthdays, her actual birthday and an official birthday marked every summer by the Trooping the Colour ceremony.
The curious decision to give monarchs two birthdays dates back to Edward VII, who was born on November 9 but celebrated the birthday in May and June as the weather was better during these months for outdoor events.
As the Queen celebrates her 91st birthday, here's a look at Elizabeth II in numbers.
- 1 - ranking in the list of world's longest-serving current monarchs. She moved to first place after the death of the King of Thailand in 2016.
- 3 - number of dogs the Queen has left - one corgi, Willow, and two dorgis, Candy and Vulcan.
- 4 - children - The Prince of Wales, the Princess Royal, the Duke of York and the Earl of Wessex.
- 8 - grandchildren - Peter Phillips and Zara Tindall, the Duke of Cambridge and Prince Harry, Princesses Beatrice and Eugenie, and Lady Louise Mountbatten-Windsor and Viscount Severn
- 5 - great grandchildren - Isla and Savannah Phillips, Prince George and Princess Charlotte, and Mia Tindall.
- 13 - prime ministers in office since the start of her reign. The first was Winston Churchill (1951-55).
- 16 - number of countries of which she is monarch - the UK and 15 Commonwealth realms.
- 16 - general elections during the Queen's reign so far. The upcoming June 8 vote will be the 17th since she acceded to the throne.
- 21 - age when she married the Duke of Edinburgh in November 1947.
- 23 - number of waxworks Madame Tussauds has created of the Queen.
- 22 - age when Princess Elizabeth had her first child, Prince Charles
- 25 - age when she became Queen on February 6 1952.
- 37 - age when the Queen had her last child, Prince Edward, in 1964
- 65 - years on the throne so far. The Queen reached her Sapphire Jubilee in February 2017.
- 70 - years of marriage the Queen and Duke of Edinburgh are due to celebrate this November - their platinum wedding anniversary.
- 72% - proportion of her life that Elizabeth II has been Queen.
- 601 - charities, organisations and military regiments of which the Queen is patron. She handed over 25 patronages last year.
- 660 - investitures - the Queen has personally held more than 660 investitures since the start of her reign.
- 23,816 - days on the throne on April 21 2017.
- 1.45 million - approximate number of people who have attended a garden party at Buckingham Palace or the Palace of Holyroodhouse since 1952.
- £1,771,441 - the Queen's earnings from race horse wins since 2013 in GB flat races.
- More than 3.75 million - items of correspondence the Queen has received during her reign.
- £340 million - the Queen's wealth, according to The Sunday Times' Rich List.