The biggest local Earth Day activity in Greater New Haven is the Rock to Rock Earth Day Ride, a fundraising event for a wide range of nonprofits.
Another big event is the March for Science, the goal of which is to call for public funding of scientific research and education, to promote empiricism and objectivity in regards to all fields of science, and to convey the nonpartisan nature of the scientific method. This march (some are really rallies and fairs) will be held in various locales:
New Haven, starting at 2:00 at College Woods Pavilion, East Rock Park – speakers and actual march
Hartford, 12-3 rally at Mortensen Riverfront Plaza
East Haddam, 10-4 Science Fair at the East Haddam Grange
Southeastern CT, 11-1 teach-in and march starting from Hole in the Wall Beach along the Niantic Bay Boardwalk in East Lyme.Washington, DC, buses leaving from Hartford just after midnight
For other Earth Day events (not all of them on Earth Day itself), see this list compiled by the CT Dept. of Energy & Environmental Protection. Other events in New Haven area:
For those who want to get earthy on Earth Day, you can plant saltmarsh grass to help restore the eroding shoreline at Stratford Point, April 21-22, 11-6. Also beach cleanup and nature walks. Sponsored by the Biology Dept. of Sacred Heart University.
Please add in other events as comments.