From Timothy McNulty

When you're watching the 12th District special election returns come in tonight, here are the four biggest counties (by the # of registered voters) to keep an eye on: Cambria, Fayette, Washington and Westmoreland. (Especially Westmoreland, which has about 25% more voters than Washington Co, for instance.)

Here are the state's official registration numbers for the 12th, courtesy of Charlie Young at the Pa Dept of State.