Peterborough City Council has one of the highest number of data breaches of any council in the UK.
New figures from the privacy campaign group Big Brother Watch show there were 160 cases between 2011 and 2014.
Incidents include correspondence sent to the wrong people and inappropriate access to information.
Northamptonshire County Council recorded 9 cases in that time – one of the lowest number of breaches in the country.
In Daventry, one of 6 cases recorded involved seven planning applications on an unencrypted CD going missing.
There were three breaches in Kettering and one in Wellingborough.
The local authorities in Corby, East and South Northants and Northampton recorded none.