The Cornish comic died on December 14 at the age of 73 after contracting Covid-19.
Real name Geoffrey Rowe, the comedy star built his name in the 1980s and 1990s, only announcing his retirement in 2020 after almost 50 years of touring.
A funeral procession was due to set off from his club in Lewdown, Okehampton, at 10am on Monday, and is expected to travel through Lifton before going on to Truro where a procession will be held at the War Memorial.
The service, at Truro Cathedral, will begin at around midday and conducted by the Reverend Canon Alan Bashforth and Reverend Tim Hodge.
A eulogy will be read out on behalf of Jethro’s family, and speakers will include his long-time agent John Miles and stand-up comic Jim Davidson
Hymns including The Old Rugged Cross and the traditional song Trelawny will be sung, accompanied by Cornish folk band The Oggymen.
When he died, Jethro was double jabbed and had had a booster vaccination, the PA news agency understands.