Thirty-five buildings in the massive complex, one of the largest housing developments in the country, were affected.
Some residents reportedly got stuck in elevators when the power went out around midnight. Power began to come back about 3 a.m.
Co-op City has its own power plant to generate electricity, but Con Edison had to step in after both the main and backup systems failed.
The cause of the outage was not immediately known. Con Ed will supply power until the problem is fixed.
Seven people had to be treated for minor injuries like chest pain and shortness of breath. Four were taken to area hospitals, but everyone is expected to be okay.
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