Commonwealth Edison says electricity rates for its residential customers are rising 38 percent on June 1.
The company says the Illinois Power Authority set the company's cost per kilowatt hour at just over 7 ½ cents, up from 5 ½ cents in 2013.
ComEd spokesman David O'Dowd said the power authority buys electricity on behalf of the northern Illinois utility.
Power costs represent about two-thirds of a customer's bill.
The other portion deals with delivery costs, which also have been rising. The average bill increased an average of $5.50 per month in January after ComEd received permission to charge more for distribution to help offset its costs to modernize the power grid.
ComEd has asked for another distribution increase starting in January.