The storm was blamed for at least 15 deaths: nine in Virginia, two in Maryland and one each in North Carolina, Pennsylvania, New Jersey and Rhode Island.
The storm ploughed into North Carolina's Outer Banks on Thursday with winds of about 100 mph and moved across Virginia, West Virginia and Pennsylvania yesterday as its winds eased to around 35 mph just below the threshold for a tropical storm. Isabel dumped up to four inches of rain in Pennsylvania before moving toward Ohio, and was expected to dissipate in Canada by Saturday.
Michael Brown, director of the Federal Emergency Management Agency, said Isabel had inflicted the worst damage along the Outer Banks.
"Our concern down there is we have about 4,000 people who refused to evacuate. We're getting in to make sure they're OK," he said on ABC's Good Morning America.
In Baltimore, 34 people were rescued from their homes, some by boat, in a neighbourhood where waist-high water flooded some streets, Mayor Martin O'Malley said.
The federal government shut down for two days. Offices, monuments and subway tunnels in Washington were all but abandoned, frustrating tourists. Some were surprised that monuments and museums were closed on Thursday, hours ahead of the storm.
FEMA's Michael Brown cautioned that residents in Isabel's path should keep their guard up, with flood waters moving into tributaries throughout the day. "So people, just because they see blue skies, should not think, 'Oh this storm is gone and the aftermath is over with.'"
With mid-Atlantic states left sodden by an unusually wet summer, the winds toppled trees and rains flooded creeks and low-lying areas.
In Middletown, New Jersey, Isabel sent a tree crashing through the roof of Jean Paul Zammit's house.
"It was a just a big bang and crack, and the ceiling falling down and everything falling down," said Zammit, who was sitting in his living room when the roof caved in.
As much as 5½ inches of rain fell on West Virginia far less than the original forecast of a foot. Flood warnings for parts of the state were cancelled.
In Virginia alone, more than 1.5 million people lost power and more than 16,000 people filled evacuation shelters. Six people were killed in a pair of weather-related traffic accidents in the state. Two were killed by falling trees. One man drowned while canoeing.
"Virginians need to realise that they're in for a tough couple of days," said Governor Mark R Warner.
Some of the worst flooding was along the Chesapeake Bay, where an 8.2-foot storm surge sent water into low-lying areas, particularly Norfolk and Portsmouth.
Along the York River in Gloucester County, authorities rescued eight people stranded on a small island surrounded by raging currents. Streets were flooded in Alexandria's colonial Old Town district in Virginia.
President Bush declared major disasters in North Carolina and Virginia, ordering federal aid to both states. The governors of Pennsylvania, West Virginia, Maryland, New Jersey and Delaware declared state emergencies.
Maryland Governor Robert Ehrlich said flooding, whether from storm surges on the Eastern Shore or heavy rainfall, was "the number one danger".
In Baltimore, the storm blew down three buildings that would have to be demolished and downed trees and utility lines. The storm knocked out generators at two water treatment plants and a sewage treatment plant in neighbouring Anne Arundel County.
The storm spared much of North Carolina the kind of flood damage it experienced from Hurricane Floyd in 1999. The storm flooded some low-lying areas and knocked out electricity for hundreds of thousands, but it didn't appear to pack the same destructive punch as Floyd, which left 56 dead and a wide swath of the state underwater.
On isolated Ocracoke Island along the Outer Banks, about 15 people gathered at Howard's Pub to ride out the storm.
"Isabel's eye passed right over us," said Buffy Warner, the pub's owner. "It was so dramatic. The rain was actually driving horizontally with these incredibly dark skies and no visibility. Then, within about 60 seconds, the sky became bright white."
A utility employee in North Carolina was electrocuted while restoring power. Most of the other storm-related deaths were from falling trees or car accidents.
A man in Rhode Island drowned after he was swept into the ocean by a giant wave while walking along the shore.