The sightings were logged by 2,122 participants.
The most commonly spotted butterfly in the county was the Small White, followed by the Gatekeeper in second place and the Large White in third.
Professor Richard Fox, head of science at Butterfly Conservation, said: “Adult butterflies love hot, sunny weather for flying, feeding and breeding, and that’s exactly why people saw so many this summer.
“However, the very same weather that made it a good year for butterflies – lots of sunshine and very little rain – could mean we’re actually on course for a population crash, which could take years to recover from.”
The charity identified the Painted Lady as a standout species this year, with 1,234 sightings in Hertfordshire alone.
Nationally, Painted Lady numbers were up 335 per cent compared to last year, in what has been dubbed a ‘Painted Lady summer’.
These butterflies undertake a remarkable multi-generational migration from Africa to the UK, crossing the Sahara Desert and Mediterranean Sea.
While high butterfly counts brought cause for celebration, experts have warned of a potential decline in populations next year.
Prolonged drought conditions in 2026 meant that many plants required by caterpillars withered before they could complete their development.
Butterfly Conservation fears the full impact of this could become evident in 2027.
The charity is encouraging residents to take action in their gardens this winter to help support butterfly populations.
Recommended steps include planting more trees and shrubs such as holly, ivy, and buckthorn, which provide food and shelter for caterpillars and adult butterflies.
Setting up water butts to collect rainwater for use during dry spells is also advised.
In addition, leaving patches of grass uncut can create cooler, damper microclimates and provide important food plants for caterpillars.
Butterfly Conservation research has shown that gardens with long grass can attract up to 93 per cent more butterflies and a greater variety of species.
The Big Butterfly Count will return in 2027, running from Friday 9 July to Sunday 1 August.