Thousands of letters will be sent to Corby residents in July after changes to modernise the way people register to vote.
They no longer apply to register to vote as a household but as an individual.
Of the 48,000 people registered to vote in the borough, 42,000 will be transferred automatically.
The remaining 6,000 are to be sent a letter explaining what they must do.
Norman Stronach, electoral registration officer at Corby Council, said: “If you are not on the register you can’t vote and won’t get a say in how the country, or your council is run.”