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From Connecticut Secretary of the State:
With Primary Election Day on August 14th fast approaching, and following several media reports about increased interest in the upcoming elections and increased voter registration in Connecticut, please note that the deadlines to register in a party in time to vote in this year’s primary are also approaching.
The deadline for new or unaffiliated voters to register in person with the local registrar of voters or town clerk of the town of residence is noon on August 13th.
The deadline for new or unaffiliated voters to register for the primary by mail is August 9th (postmarked). New or unaffiliated voters can also register at myvote.ct.gov/register by 11:59pm on August 9th, or at the DMV by the close of business on August 9.
The deadline to change parties in order to vote on August 14th in the new party has already passed.
Please note that there is no Election Day Registration for Primary Elections, only for General Elections.