The details of nearly 3,000 people are stored on a Cumbria County Council database because they're deemed "a threat" to staff.
Figures from the Press Association show the vast majority of entries are violence-related, with most of the rest about people with dangerous animals.
It means when the authority comes into contact with them they're flagged up as a potential risk to worker safety.
Nationally, 25,000 people are on so-called cautionary contacts lists - there's concern some cases may not be current, with some lying on file for decades.
In Cumbria, the average stay on the list is almost four years.
A Local Government Association spokesman said: "Councils have a duty of care to their employees to ensure they are safe and aware of risks when carrying out their work.
"Local authorities keep cautionary contacts lists purely to protect staff who are in regular contact with local residents and businesses.
"Councils take their responsibilities under data protection law very seriously and, despite limited resources, are investing in robust systems to further safeguard confidential information prior to the implementation of the General Data Protection Regulation in May 2018.
"As far as we are aware, local authorities have complied with the law in the way they are recording data while maintaining these lists."
Cumbria council recorded 2,924 people on its system. The overwhelming majority (2,473) were violence-related records, while 263 were for a dangerous animal. The council said people spent an average of 195 weeks on its system.
Lancashire council had eight records for Adult Social Care users, aged 25 to 75.