Buckinghamshire has lost almost 40% of its firefighters since 2010, Home Office figures reveal.
The Fire Brigades Union has lambasted the "appalling cuts" to fire services across the country, which it says are putting public safety at risk.
In the Buckinghamshire and Milton Keynes Fire and Rescue Service, the number of full-time equivalent firefighters fell from 556 in 2010 to 345 in 2018 - a drop of 38%.
This is one of the biggest cuts of any fire and rescue service in England.
Of these, 23 were lost in the 12 months to March 2018.
Across England, the number of firefighters has fallen by more than 22% since 2010, from 41,632 to 32,340, and there are now 45 fewer fire stations.
The average time taken to respond to the most serious incidents increased by more than 30 seconds over the same period.
Response times for the Buckinghamshire and Milton Keynes Fire and Rescue Service were 12 slower in 2017-2018 compared to 2016-2017, but were quicker than in 2010.
However, at an average of 10 minutes 13 seconds, the average response time is still slower than the England average, which stands at 8 mins 45 secs.
The Home Office said local factors could affect response times, and that there is not a straightforward link between response times and the outcomes of a fire.
Matt Wrack, FBU general secretary, said there was a clear link between slower response times across England and government cuts.
"Year on year we are seeing appalling cuts to the service," he said.
"Understaffed fire stations across the country struggle to provide a 24-hour service to their community, with the starkest effect outside of cities.
"Fire and rescue services are expected to do more with less and it is only down to the dedication of fire and rescue staff that the service is performing at all.
"The service is at breaking point. Public safety is being put at risk.”
Fire and rescue services in metropolitan areas such as Manchester and Liverpool have seen the biggest cut in firefighters.
However, the biggest slow down in response times has been in non-metropolitan areas, where they have gone up by an average of almost one minute.
A Home Office spokesperson said: “The Government is thankful for the continued tireless efforts of firefighters across the country.
“There has also been a long term downward trend in both fires and fire deaths for many years, recently reaching historically low levels, and we are confident that fire and rescue services have the resources they need to do their important work.”