Most of those were in Louisiana, where utilities reported nearly 240,000 people without power as of Monday morning. More than 11,000 were without power in Mississippi.
Meanwhile, inspectors from the Federal Emergency Management Agency are out trying to get a handle on losses. FEMA opened a recovery center in Pascagoula, and officials say more centers could open in the coming days.
Crews also are still working to clear debris left by Isaac, mostly downed trees and power lines. So far, state workers in Louisiana have cleared 130 miles of roads.