Voting reminders are being sent to 25,000 homes in Dacorum because the council is still waiting on the return of electoral registration forms.
Over the summer, households were sent the annual household enquiry form listing all those who are registered to vote at that address.
The form must be updated and returned to Dacorum Borough Council so that anyone not already registered to vote can be told how they can.
Some wrongly believe that paying council tax means they are registered to vote.
So far, 40 per cent of homes have yet to return the form but the council says it is easy to confirm details by phone, text or online.
If there are any changes or additions, such as new residents or children aged 16 or 17, they should be marked on the form and returned.
Those who have not received or have lost the form can call 01442 228000 and ask for electoral services, email firstname.lastname@example.org or visit www.dacorum.gov.uk/registertovote