Peco ranked the event as the largest winter power outage in its history, second overall to 2012's Hurricane Sandy.
Despite the best efforts of its crews, Peco officials said, some customers in the areas hit hardest by Wednesday's ice storm, primarily in Chester and Montgomery Counties, will not regain power until early next week.
Staff at emergency shelters prepared for additional guests.
"People thought that if I just stick it out for a couple of days, this will be passed," Glenn Cannon, director of the Pennsylvania Emergency Management Administration, said at a Friday news conference outside a shelter in West Chester. "People have reached the point where they're a bit frustrated, and they also realize, 'I just can't do this anymore.' "
Cannon said he anticipated a "substantial" increase in check-ins over the weekend. In addition to the West Chester facility - where more than 180 people spent Thursday night - the Red Cross is also running shelters in Montgomery and Bucks Counties.
A quarter of Montgomery County and 22 percent of Bucks County were still without power at 7 p.m. Friday.
The West Chester shelter is set up for 400 visitors, but could be expanded to house up to 1,300.
Some residents were determined to ride out the outages at home.
On Friday afternoon in West Caln Township, Chester County, Phil Kirby pulled into his driveway hauling a trailer full of firewood - for the wood stove and fireplace that have heated his home since Wednesday.
Despite both, Kirby said, the house was only at 52 degrees.
"I'm seriously thinking about getting a generator. But they're not cheap to buy," Kirby said as generators hummed throughout the community, which was 60 percent without power.
Renée Cardwell Hughes, CEO of the Red Cross of Southeastern Pennsylvania, urgently encouraged those without power to stay somewhere warm.
"We are a strong, proud people in Southeastern Pennsylvania, and so we tend to think that, 'Oh, it's not that bad. It's not that cold. We can handle it,' " she said. "Hypothermia can set in in less than five minutes. Please, the shelter is warm. It is safe."
Officials said concerns about pets were keeping many residents from going to a shelter. But they stressed that Red Cross facilities were pet-friendly.
Robert Taylor, 88, has been staying at Barkley Elementary School in Phoenixville since Wednesday night, after a police officer knocked on the door of his apartment on Nutt Road. A maintenance worker in his building gave him a spare cellphone to hold onto, though he said he didn't know how to use it.
Taylor said he was enjoying himself at the shelter, where two young children drew pictures of a meadow and leaping dolphins for him.
"I told them, when I get home I'm going to put them on my fridge," he said. "And I will."
Other families, such as the Hegeduses of Huntingdon Valley, were staying with relatives.
At lunchtime Friday, the family sat at a back table at the Chick-fil-A on Easton Road in Warrington, Bucks County, which was jammed with some men from the nearby military base and a few senior citizens, but mostly families with children.
Lots of children. Almost as many as there were ketchup packets in the place.
Life normally is chaotic for parents Tom Hegedus, 43, and Bianca, 46. They likened their usual life with three young sons - twins Connor and Kevin, 8, and 9-year-old Brian - to the Three Stooges. In fact, one of the twins had a sling on his arm after tussling with the other over a video game.
They had stayed in their house until about noon Wednesday, after the electricity went out at 7 a.m. Then, they packed up the children and their golden retriever to stay with Tom's parents, who live nearby.
Tom was getting along with his parents just fine, though he hasn't lived with them for this long since he was in his 20s.
"My in-laws are terrific," Bianca said.
The children love their grandparents, who have a bigger yard - better for playing, which is more important since they had not had school much of the week.
"I want to stay at Mimi's and Pop-Pops'," said Connor. "It's funner."
As the restoration effort continued, Federal Emergency Management Agency crews were readying 95 industrial generators on 21 flatbed trucks at the Air National Guard base in Horsham that will be used to bring power to places such as hospitals and water-treatment facilities, according to a news release.
State officials said Friday that the ice storm presented unique challenges and left the state's power grid and infrastructure more damaged than Hurricane Sandy had. Cannon, of PEMA, said that when power-line poles blown down during the hurricane were fixed, that restored power to large areas. But in this storm, he said, there are "many more spot repairs" to downed wires that feed power to fewer buildings. "There are literally thousands of places like that."
He urged residents heading to shelters to bring "patience and understanding" with them.
"We know these are difficult situations," Cannon said. "The good news in this event is, as soon as the power's up, you can go back home."
Inquirer staff writers Ben Finley and
Jessica Parks contributed to this article.