A 41-gun salute was fired at the Tower of London while other gun salutes echoed across Edinburgh, Cardiff and Belfast on the anniversary of Queen Elizabeth II's coronation in 1953.
The Queen and Duke of Edinburgh were driven onto the course with racegoers cheering as the Royal motorcade reached the winning post.
Also joining the Queen in her royal box was Sophie, the Countess of Wessex, the Duke and Duchess of Gloucester, and Prince and Princess Michael of Kent.
The Queen rarely misses attending the Epsom Derby, which is one of the highlights of the racing calendar. Unlike last year, the Queen does not have a horse entered in the Derby, or the other six featured races.
This year, however, the Jubilee celebrations created an extra air of excitement, despite the grey and drizzly conditions.
At Windsor Castle, 21 mini cannons were fired to mark the start of the Diamond Jubilee weekend.
In London The King's Troop, Royal Horse Artillery, fired a 41-gun salute. It followed the Major General's Parade, which drew large crowds to Horse Guard's Parade.
After the parade 72 horses and six First World War era 13-pounder gun carriages passed along Horse Guard's Parade for the salute, which started at 1pm, lasting just over seven minutes.
The Coronation Gun salute is normally fired from Green Park, but Horse Guards Parade was used as part of a series of public events in the Royal Parks to mark the Diamond Jubilee.
Similar 21-gun salutes were also carried out at Edinburgh Castle, Cardiff and Belfast.
The King's Troop, Royal Horse Artillery, will return to Horse Guards Parade on Tuesday, when they will fire a 60-round Royal Salute from their six guns as the "heart beat" to the Diamond Jubilee Procession.
The first gun will fire when the Queen leaves Westminster Hall accompanied by the Household Cavalry Mounted Escort and continue to fire throughout her return journey to Buckingham Palace.
The guns will fire at 60-second intervals for one hour - one round for each year of the Queen's reign.
Further up the Thames more than 1,000 boat crews were putting the finishing touches to their vessels ahead of the Thames Diamond Jubilee Pageant on Sunday.
The flotilla is due to escort the Royal barge along the Thames and is expected to draw large crowds in London. More than 20 vessels from the Royal National Lifeboat Institution are being drafted in for the occasion to help with safety on the river.
Final preparations were also underway for street parties that are taking place the length and breadth of the country.
At Chatsworth Estate in the Peak District a 300 feet long picnic table was set up in the gardens and a special Coronation exhibition was opened, displaying the robes worn by four generations of the Cavendish family at the Queen's Coronation.
Hundreds of visitors to Chatsworth joined in the 1950s-style, giant street party in the garden, which had traditional village fete games such as a coconut shy and a test of strength.
David Jackson, who lives close to the estate, said he and his wife came to the stately home to celebrate the jubilee and "join in the fun with everybody else."
He said: "It's very special for the Queen, that's why we're participating: just to make fun and have a really happy day."
Maxine Siddall, from Matlock, was there with her children because she heard there was a party with lots of things to do for her family.