Most coal-fired power plants are at least as old as I am. But I never spew mercury into the air.
The Energy Information Administration published a couple of charts that have the energy/environment blogosphere talking. Above, see the amount and source of energy that came online in the United States by year. The ‘50s, ‘60s, ‘70s and ‘80s saw tons of coal plants built. Not a ton after that thanks, as Brad Plumer wrote, to cost, regulation, and advocacy.