California, which has 55 electoral votes, has been in the compact since 2011.
Illinois, which has 20 Electoral College votes, was the third state to join the compact in 2008.
Hawaii and its four electoral votes are in the compact.
Massachusetts, which has 11 Electoral College votes, joined the compact in 2010.
Massachusetts' next-door-neighbor Rhode Island, which has four Electoral College votes, is also in the compact.
Connecticut, which has seven electoral votes, joined the compact in 2018.
And Washington, DC, which has no voting representatives in Congress but three Electoral College votes, joined in 2010.
New Jersey, which has 14 Electoral College votes, became part of the compact in 2007.
Its neighbor New York, which has 29 Electoral College votes, joined the compact in 2014.
Maryland, which has 10 Electoral College votes, has been in the compact since 2007.
Vermont, which has just three Electoral College votes, became part of the compact in 2011.