In Georgia, utilities reported about 950,000 customers without power.
FPL, the biggest power company in Florida, said the company's system will need to be rebuilt, particularly in the western part of the state.
Irma's top sustained winds are 35 miles per hour (55 kph), and it is moving northwest at 15 miles per hour (24 kph).
Hurricane Irma: How those receding waters may have saved Tampa
Most of the power losses were in Florida, but losses in Georgia, which were at about 90,000 as of 6 a.m. ET (1000 GMT), were expected to increase as the storm moved north.
The storm has slowly weakened as it traveled up the Florida coast, and was officially downgraded on Monday morning to a tropical storm.
The forecast track has the center of Irma heading into southern Georgia this afternoon and moving through eastern Alabama tonight and Tuesday.
Residents who fled the Florida Keys in anticipation of Hurricane Irma's wrath were told they could not return to their island homes on Monday, news that angered evacuees anxious to get back to assess the damage. This raised the overall death toll from Irma's powerful rampage through the Caribbean to 38. The plant's other reactor, Unit 2, continued to operate at full power.
Utilities are pooling workers from more than two dozen states to help fix infrastructure in Florida, some which are coming from making repairs after Hurricane Harvey hit Texas and dumped record amounts of rain, the WSJ reports. The officials also instructed residents to beware of downed power lines.
- In Venice, Florida, the water plant was shut down after it was damaged by the storm. In the Atlanta metro area, about 496 stations, or 12.2 percent, were out of gasoline, according to information service Gas Buddy.