The final two customers left without electricity after last week's storm had power restored early Sunday morning.
"We've reached 100 percent," said ComEd spokesman Tony Hernandez.
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Outages particularly ravaged Lake County after storms struck last Monday morning, leading officials there to declare a state of emergency.
At the outage's peak, 850,000 ComEd customers were without power across the region.
ComEd struggled with gaining access to the final two customers, which delayed restoring their power, Hernandez said. One was a single-family home near Mundelein in Fremont Township. The second was a Canadian National Railway Co. building, also in Lake County.
By declaring a state of emergency Wednesday, the county made it easier for neighboring municipalities to share resources as cleanup commenced.
ComEd is now turning its attention to an expected spike in power consumption from air conditions going full throttle to battle a heat wave forecasters say will bring 90-degree highs every day this week.