Power was largely restored in areas hardest hit by last Tuesday's tornadoes.
Eversource said the damage from the storm surpassed that of storm Sandy in 2012.
Power was back on at Oxford High School on Monday morning; however, it wasn't for 9 percent of the rest of the town.
Many roads also remained blocked.
That forced officials to close schools for yet another day. A decision on when students could return to class could come later on Monday.
Eversource said it tried to get the power back on by last night for most customers. Its new estimate is tonight, except for those homes and businesses that were too badly damaged and will require additional work to safely restore electricity.
Veteran utility workers described the damage as the worst they had ever seen.
Oxford was one of the towns hit by one of three confirmed tornado touchdowns, according to the National Weather Service. A fourth contact was also confirmed, but was on the Barkhamsted Reservoir.
At one point after the storms wrapped up, more than 150,000 customers were without power.
As of Monday morning, that number was down to about 5,700 for Eversource, mostly in New Fairfield and Brookfield.
For United Illuminating customers, only 260 were powerless, mostly in Hamden.
Eversource said Sandy's strongest winds were 85 mph. Tuesday's tornadoes had 110 mph winds.
It also said Sandy broke nearly 1,700 utility poles. More than 1,800 broke last week.
Finally, Eversource revealed than Sandy brought down 105 miles of power lines. After Tuesday, 288 miles of lines were down, which is twice the length of the State of Connecticut.