Irene made landfall along the coast of New Jersey near Little Egg Inlet, just north of Atlantic City, around 5:35 a.m. The estimated intensity of at landfall was 75 mph.
It was the second time Irene made landfall since slamming into North Carolina Saturday.
While Irene's strength has declined and evacuated residents are returning home, government officials warned the public that the storm still poses safety dangers.
"We still have a ways to go with Irene," Napolitano said at Federal Emergency Management Agency (FEMA) news conference.
Some areas are still prone to tidal flooding and heavy rains will be the ongoing issue as the storm passes through New England today to eastern Canada overnight, FEMA officials said.
Officials said it will take time to assess total damage costs but Peter Morici, a professor at University of Maryland, said the cost of Irene could surpass that of Hurricane Katrina.
"Revised estimates of the direct damage caused by Hurricane Irene are in the range of $20 billion. Add to those the loss of about two days economic activity, spread over a week, across 25 percent of the economy, and an estimate of the losses imposed by Irene is about $40 billion to 45 billion," Morici said.
Loss of Life
At least 20 people have reportedly died as a result of Irene's assault on the East Coast, including victims of car accidents and falling tree limbs. The storm victims include two children: an 11-year-old boy in Virginia, and a 15-year-old girl in North Carolina.
The Associate Press contributed to this report.