We summited Connecticut the day after we did Massachusetts. We drove down from Greylock and followed directions approaching Frissell from the north via the Mt. Washington Road. It is very easy to find your way, however we were following directions that said to look for the stone state line marker which we never found. We wound up going past the parking lot we wanted because the directions also said a white gate and the actual gate is clearly not painted and is metal. So after turning around a few times I decided we had to be in the right spot and we started up the jeep road. The jeep road is easy to follow although it was covered in a creek for a stretch. We came across the Mt. Frissell shortcut trail after the 2nd creek at a small cairn. The trail was overgrown and very muddy so we continued up the jeep road. At the top of the ridge we took the first right on an unmarked trail, then at the next intersection took a left, and then hit the red blazed trail where we took a right. A short while later we were at the tri-state marker. From there you continue up the red blazed trail over some granite boulders and up to the "green stake". I found this hike to be much more enjoyable than other people have said and the "summit" was nice. I think the mileage is longer than advertised as it took us 3 hours to make the round trip with a 5 year old (whom I had to carry at several points as he was getting tired).
Here are the instructions to the trailheads from I-90 (modified by me to work better):
1. Take MA exit 2 towards US-20, keep left towards US-20 / RT-102
2. Turn left onto US-20 and then right to RT-102
3. Keep straight onto US-7 South and stay on US-7 South
5. Turn right onto SR-41 South (not North)
6. Turn left to stay on SR-41 South and then immediately to the right onto Mt Washington Rd.
7. Continue straight (road name changes to East Street at some point). You pass the Forest Headquarters (on your right), then the road becomes unpaved. Keep going until you see a large parking area and the AMC sign on your left. The first trail (red blazed over Round Mountain and Mt Frissel) starts from the right. A stone state line marker is reported to be here as well although we never saw it
8. Go 1.2 mile past the AMC parking area until you see a small parking area on your right. There is a 2nd small parking area immediately after it that has a metal gate back and to the right (which you cannot see until you stop and look backwards). This is the jeep road that you want to follow. If you hit a lake on the right you went to far. Turn around and go back 2 miles to the parking area.