If you are truly going to the Northwest corner (as opposed to Litchfield), you might try the West Main Cafe in Pocket Knife Square in Lakeville. They do a very nice job. Food has a slight Asian bent to it. Their green salad starter is fantastic and one I would love to eat everyday. Very simple bibb lettuce with an asian vinaigrette and little fried onions or even shallots on top. They serve it in a bowl with chopsticks. Steaks are good. Fish is good. There is a bar menu in front and a more elaborate menu in the dining room. Last time I was there service was very off..it seemed like they were understaffed.
There's also the Boat House Cafe across the street. Nice fish. Sushi is even ok. I am mindful of the sauces as they often go overboard. Very friendly service. Good wines. Good desserts.
Here are some favorites of my friends and family: River Grill in West Cornwall (just east of the covered bridge)-extremely well prepared and creative food which, perhaps unfortunately, is in a restaurant/upscale food store. A few weeks ago, we had outstanding diver scallops in a lucious light sauce and boar that was excellent. Desserts are not up to the standards of appetizers and main courses. For the northwest corner, this is as could as it gets. Go-we're afraid it won't survive the long winter! Woods in Bantam-an excellent BBQ joint on Rt 209, about 1/4 mile south of 202. All the standards you'd expect in such a place, unusually well prepared for this part of the country. You probably know of the West Street Grill in Litchfield; service can be pretentious, but the food is quite good. And if you want a beautiful setting, with excellent service and aren't put off by New York prices, the Mayflower Inn in Washington is really quite good.