The Prime Minister and his wife are said to be hosting family and friends at 18th-century Daylesford House, in Gloucestershire.
But it appears that the majority of guests will be friends, rather than politicians or aides.
Michael Gove, who was sacked after telling Mr Johnson to step down from his Downing Street role this month, is reportedly among those who have been culled.
But Zac Goldsmith, a key ally and friend of Mrs Johnson, is in line for a prominent role.
Prime Minister Boris Johnson and his wife Carrie
POOL
Former Cabinet minister Michael Gove
Danny Lawson
Photographs of Daylesford House show a huge white marquee topped with bunting in the property’s expansive grounds.
Owned by Lord Bamford, the Grade I-listed mansion has been found as a replacement to Chequers – where the Johnsons had originally planned to host the party.
The Tory peer, chairman of construction equipment manufacturer JCB, has donated millions to the Conservative Party.
Mr and Mrs Johnson married in a low-key private ceremony at Westminster Cathedral last year.
A small group of family and friends attended the wedding, organised in strict secrecy, followed by a reception in the gardens of 10 Downing Street.
It was known Mr and Mrs Johnson planned to have a larger celebration this year after coronavirus restrictions had been relaxed.
Lord Bamford is covering at least some of the cost of the party, the Mirror reported, quoting unnamed sources.
