People in Bourne and the Deepings are being urgeed to register as a voter by South Kesteven District Council.
Registration forms have been sent to homes across the area ahead of the biggest change to registering electors for more than 100 years.
The council is bringing in an Individual Electoral Registration system so that people now need to register individually as voters, instead of by household as before.
District council leader Linda Neal said: “It is really important that residents respond to the letter if it asks them to take action.
“You need to register in order to be able to vote and the council is focusd on ensuring that people have the information they need to take action.”
About 10,500 people in South Kesteven will need to re-register, while others will be transferred automatically to the new register.
For more information about the changes, visit www.southkesteven.gov.uk/IER