Via Dave Roberts, Coal Industry whitewashing group America's Power shows just how dependent America is on coal to provide electricity. Indeed, coal is the plurality source of energy in 30 states, and accounts for at least 20% of electricity in all but 12. They're trying to convince you that coal power is the reason that some states have lower electricity prices, but it's worth pointing out that (a) a number of other factors come into play, and (b) the end result of any climate change legislation will be to raise the price of polluting energy sources like coal.
Below is a nice map showing that coal is the dominant source of energy primarily in the Midwest and Interior Plains. Western states use more hydroelectricity and natural gas; the Northeast and South have more nuclear plants.