3 of the 4 go-kart venues Go Karting USA tracks in Connecticut host birthday parties, based on what each venue publishes and what visitors describe. They sit outside the state's main metro areas, so check the addresses before you commit to a drive.
Party bookings work differently from walk-in racing: expect a reserved room or area, a set number of races per guest, and a deposit. Weekend afternoon slots go first, so start calling two to three weeks out — and confirm the height rule for the youngest guests before invitations go out, since it varies venue to venue.
Supercharged Indoor Karting and Axe Throwing, On Track Karting's GO TIME, MONZA World Class Karting at Foxwoods — all listed below with ratings and locations.
Two to three weeks for a weekend slot, more around school holidays. Party rooms and group race slots are reservation-based at essentially every venue, and afternoon weekend times fill first.
Go Karting USA lists 4 operating tracks in Connecticut — see the full Connecticut guide for all of them, not only birthday parties venues.