Spokesman Ben Armstrong said they hope to have power back for most by Friday.
A record-number of people lost their power across the region thanks to a significant ice storm and power officials warn it could be days before everyone has their electricity back.
"Based on the current conditions and the damage across the entire region, we believe service for the majority of customers will be restored by Friday night," said PECO spokesman Ben Armstrong. "However customers in more heavily-damaged areas will be without power through Sunday."
PECO Energy, the largest power provider in the Philadelphia region, told NBC10.com the storm was the second worst in their history and worst winter storm outage ever with more than 600,000 customer without power at the height of the storm. More than 80 percent of customers in Chester County alone were left in the dark.
Adding PECO's outages with other Pa., N.J. and Del. power company issues, more than 700,000 customers lost power at some point over the course of the storm.
By Thursday evening, there were more than 336,000 customers without service after many crews worked overnight in cut-and-run mode.
"While it's down from the 623,000 customers who were impacted... we really want people to understand that there is significant damage that needs to be repaired," said spokeswoman Cathy Engel Menendez. "We will be working on this for many days to come."
PECO, which has about 1.6 million customers in six Pennsylvania counties, says snapped power lines, icy trees and cars crashing into utility poles were the main cause of outages for their customers.
The utility dispatched an army of 3,500 utility workers -- some crews from as far away as Arkansas, Illinois, and even Canada joined PECO's repair effort, according to Armstrong.
Some people took getting power back into their own hands with nearly deadly results.
"We ended up sending about 25 people to the hospital overnight -- four of them fairly critical -- because they were using gas grills or generators inside producing carbon monoxide," said Bob Kagel, deputy director of emergency management for Chester County.
Pennsylvania counties have fared the worst in this storm. Here's the breakdown of outages from PECO and PPL Electric, which also services several Pa. counties:
Blackouts in Abington, Pa. forced Abington Memorial Hospital to switch to backup generators, hospital officials said. A spokesperson said the outage did not affect care and that the hospital remained fully staffed.
Several schools, including Villanova University and Arcadia University were closed due to a loss of power. Villanova will remain closed until Friday while power was restored at Arcadia's Glenside campus. An NBC10 viewer told NBC10 that students at Arcadia's Oak Summit Apartments stayed in the hallways due to the cold conditions.
"The school has power but there apartments don't," said Regina Bonino Miller. "Nothing is being done and there may be no power for three days and they expect them to go to class."
Arcadia posted a message on their website stating that staff at the school moved generators to Oak Summit for heat and basic lighting. They also stated that classes at the school's Glenside and King of Prussia campuses were closed.
Over in New Jersey, PSE&G said 9,180 customers, nearly all of them in Burlington and Mercer Counties, were without power at one point, that number was down to 1,432 by early Thursday evening.
In Delaware, Delmarva Power reported more than 6,100 outages in New Castle County, Del. at one point. There were about 400 outages by early Thursday evening.
Officials urge people without power to alert the utility and DO NOT call 911.
You can use the following numbers to report your loss of power or make a report through each company's website.