Around 4,700 cases of coronavirus have been linked to Boardmasters Festival.
But Cornwall leaders say they are satisfied with how the festival was organised and have "no regrets" about it going ahead.
During a briefing on Monday 23 August, public health director for Cornwall and the Isles of Scilly Rachel Wigglesworth said Cornwall now has one of the highest case rates in the country.
Previous peaks in Cornwall were 411.6 per 100,000 on July 19 and 367 per 100,000 during the January wave.
Deputy director of public health Ruth Goldstein confirmed 4,700 people who have had a positive PCR test said they attended Boardmasters festival.
About three quarters of those people are aged 16 to 21 and around 800 of them live in Cornwall.
Dr Goldstein said the Boardmasters team planned an "awful lot of measures" ahead of the festival and went above and beyond the national guidelines.
"It's a very sociable disease, it likes groups of people," she added. "We tried to mitigate and tried to reduce some of the impact."
Cornwall Council's cabinet member for adults and public health Andy Virr, said although "infections are troublesome" the cases are "not translating into a serious life-threatening illness".
"At the moment there are no regrets," he said.
Malcolm Bell, chief executive of Visit Cornwall, issued a plea for people to get vaccinated as soon as possible and keep procedures such as wearing masks and testing regularly.
He said: "You might be on holiday but the virus isn't on holiday. The virus loves a party.
"We appreciate young people have been locked up for quite a long time.
"It's a message to everybody in Cornwall, the virus is here, it's having a great summer."