Medway is the most complained about council in Kent, according to data from the Local Government Ombudsman (LGO), while Tonbridge and Malling received the fewest.
Law firm claims.co.uk investigated the number of grievances lodged about each authority from March 2016 to March 2022.
It also compared the figures to historical data to determine which councils were improving, with falling numbers of complaints, and which were seeing dissatisfaction grow.
It discovered that, over the study period, the LGO received 20.2 complaints for every 10,000 residents in Medway about the unitary authority.
The second highest number were lodged against the district council in Thanet with 19.9 complaints per 10,000 people.
The rate in Tonbridge and Malling, on the other hand, was 7.1 - and only 22% of those were found to be justified.
More than half of the complaints against Medway - 55% - were found to be valid.
A Medway Council spokesman said: "We take all complaints seriously and use the valuable feedback to improve our services.
"When mistakes are made, we listen to our customers and residents, apologise and work to put things right.
"We aim to learn from complaints and make long term improvements to our services, if a problem is identified.
"We welcome comments from the Ombudsman and work with them to ensure complaints are appropriately remedied.”
But he added that, as Medway Council is a unitary authority and responsible for more services that the district councils in Kent, it "would be inaccurate to compare us statistically to other authorities."
While coming out on top for performance, Tonbridge and Malling council's leader Cllr Matt Boughton said the authority tried to resolve an issues with residents directly.
He told KentOnline: "We take all complaints seriously and use a proven three-stage process that works well.
"While some residents may still feel unhappy with the outcome and choose to go the ombudsman, we generally find that by investigating complaints thoroughly, particularly those that have reached the chief executive for consideration, we are able to resolve most matters so that residents don’t feel the need to escalate their complaint further."
Researchers also looked at the average number of complaints for each authority in the three years up to the end of March 2019, and compared that with the previous three years.
They found Tunbridge Wells' was the most improved council, with the number of complaints per head of population dropping by 34%.
A spokesman there said: "We take complaints very seriously, we aim to learn and improve. We welcome feedback."
Thanet, Swale, Medway, Canterbury, Maidstone, Ashford and Dartford also saw proportionately fewer complaints.
Residents in Sevenoaks, on the other hand ,saw a 53% increase in the number of grievances raised with the LGO.
But a spokesman for Sevenoaks District Council said claims.co.uk had missed the point - it was not the number of complaints made against a council that was important but the number that was found to be justified.
He said: "During the period 2017 to 2022, the ombudsman upheld only eight complaints against Sevenoaks - the third lowest number in Kent over this period.
"We took every case seriously, putting in place improvements to prevent similar mistakes from being made in future.”
George Patton, a spokesman from Claims.co.uk, offered guidance on how to make a complaint.
'Naturally residents have rising expectations that their local authorities will provide better services'
He said: "Council tax has increased by an average of £67 for Band D properties this year amid the cost of living squeeze.
"Naturally residents have rising expectations that their local authorities will provide better services.
"Although taking on your council might seem daunting, it’s vital to know your right as a resident and speak out if you feel that your council has failed to deliver a service.
"Your first step should always be contacting the service provider in question and if you are not happy with the solution provided, the LGO will come as a final resort.
He said: "Be sure not to delay and lodge your complaints as soon as possible.
"Stay polite throughout the process and provide clear evidence to support your claim, As the LGO’s decision is final - your case won’t be reviewed again unless new evidence comes to light."
The full study, which covers the whole country, can be found here.
Folkestone and Hythe was not included in the study as the 2016/2017 data was not available for the council.