Dormice were only reintroduced to the Bedford Purlieus in 2001
A forest near Peterborough is now one of the top 10 breeding sites for dormice in the UK.
The little mammals were only reintroduced at Bedford Purlieus Wood nine years ago and their numbers have been checked every autumn since.
Forestry Commission ranger Cheryl Joyce said: "This count was the best we've ever had."
Dormouse numbers declined sharply after World War II as their habitat was destroyed.
In 2001, 21 pairs of captive-bred dormice were reintroduced to Bedford Purlieus Wood.
The project was run by Natural England and the People's Trust for Endangered Species.
Forestry Commission volunteers looked after the creatures, and supervised their release.
Jim Alexander, who is a retired chief wildlife ranger and now a volunteer, said: "It was important that we selected the most suitable habitat in which to place the dormouse boxes, which was one that offered a dense mature under-layer of shrubs with well-spaced mature native broadleaves."
Bedford Purlieus Wood is very good at breeding baby dormice like this
More than 40 dormice were found in the 2010 count, but it is believed that there are far more of them elsewhere in the forest.
The count can only assess dormice found in wooden nest boxes dotted around the wood.
"This is not always the most accurate way of establishing numbers," explained Jim. "As some dormice prefer to build their own nests high up in the shrubs or trees where they are less likely to get disturbed by predators.
"But at least it gave us an approximate figure to work with."
Dormice are nocturnal creatures, and are one of the few British mammals to hibernate.
They begin their hibernation in November, having increased their weight to 40g to help them make it through the winter.
They usually hibernate until March, and produce their first litter in June or July.
Habitat destruction from World War II onwards has seen their numbers dwindle.
Dormice have a novel way of dealing with wet and cold summer weather.
They save energy by going into 'torpor' - they curl up into a ball and go to sleep.
This no doubt explains why they are traditionally considered somewhat dozy.