The number of voluntary officers working for Northamptonshire Police has fallen from 722 to 377 since May 2016.
Police and crime commissioner Stephen Mold said the drop-out rate had not changed much recently but recruitment efforts had fallen.
Mr Mold said he preferred to "focus on quality, not quantity".
His predecessor Adam Simmonds had aimed to recruit 900 specials to the force but when Mr Mold took over in May 2016 he pledged instead to maintain a ratio of full-time officers to specials of about two to one.
Northamptonshire Police currently has 1,220 full-time officers.
A report due to be presented to Northamptonshire County Council on Thursday suggests part of the decline is due to the way the statistics were presented.
However, it adds 260 special constables have resigned in the past 10 months.
It listed reasons for leaving including a loss of commitment, or volunteers becoming a full-time officer or a change in work-life balance.
260
The number of specials who have resigned since May 2016
900 Adam Simmonds' target
722 Number of specials when Adam Simmonds left in May 2016
377 Current number of specials
It noted that some specials had raised concerns about equipment, particularly a lack of lockers or body-worn video equipment.
Mick Stamper, the force's head of operation policing, said many of the specials who had left "didn't meet the standard" required or had not been able to commit to regular duties.
One special constable, who spoke to the BBC on the guarantee of anonymity, said: "There are so many unhappy and unsupported and rarely valued officers.
"The lack of help and support for the special constables is mind-boggling.
"Who would want to stay and volunteer in an organisation that shows no respect or helps their volunteers."
Mr Simmonds' target was part of plans to "make Northamptonshire the safest place in England".
In an article on ConservativeHome in 2014, he said the force had "the highest proportion of Special Constables of any force in England and Wales".
In July 2013, the force employed more than 250 specials and Mr Simmonds pledged to put more "boots on pavements" by increasing their numbers.

Sam Warburton and Justin Tipuric were the flankers in the 21-16 defeat in Cardiff, with Ross Moriarty outstanding at number eight.
Moriarty was replaced in the second half by fit-again Taulupe Faletau - but ex-flanker Williams said Wales "can't drop" the Gloucester man.
"It's working at the minute," he said.
"You keep the same back row. And you've got Faletau to come off the bench."
Media playback is not supported on this device
Faletau's second-half appearance was his comeback following a knee injury suffered playing for Bath on 24 December.
Cardiff Blues' Warburton, Tipuric of Ospreys and Gloucester's Moriarty also started in Wales' opening Six Nations game - the 33-7 win in Italy.
Williams, who won 100 caps for Wales between 1996 and 2012, has been impressed with the form of 22-year-old Moriarty for club and country.
"He was simply sensational for the time he was on the park last week," Williams told BBC Wales' Scrum V programme.
"You can't drop someone like Moriarty. Again on Friday night for Gloucester against Saracens he was outstanding. If somebody's in that form just keep them going.
"There's always been a debate come Warburton and Tipuric playing together and it's been so far so good in this tournament."
Williams also believes wing Alex Cuthbert responded in style to criticism of his performance in the defeat by England with a try in the Blues' 57-20 win over Treviso.
Cuthbert missed a tackle on Elliot Daly for England's winning try in the Six Nations match and was released back to his region.
Blues head coach Danny Wilson has urged Welsh fans to back the 26-year-old wing while Williams was impressed with the performance of his former team-mate against Treviso.
"It just shows his mental strength," Williams said. "He could easily have had the week off and go and hide but he wanted to play and it was the old Alex Cuthbert.
"It was good to see him back in form."
A police force that boasted of having the highest proportion of special constables in the country has seen almost half of them leave the force.
[NEXT_CONCEPT]
Wales should select the same back row that started against England when they travel to Scotland on Saturday, says ex-captain Martyn Williams.