1810 United States House of Representatives elections in Pennsylvania

Elections to the United States House of Representatives were held in Pennsylvania on October 9, 1810, for the 12th Congress. The Federalists were in decline in Pennsylvania at this time. In six of the eleven districts there were no Federalist candidates.

Background
Eighteen Representatives had been elected in 1808, 16 Democratic-Republicans and 2 Federalists. One Democratic-Republican resigned and was replaced by another Representative from the same party, so that there was still a 16-2 division. Four of the Democratic-Republicans and two of the Federalists were "quids", a short-lived alliance of moderate Democratic-Republicans and Federalists. That was the last year in which the quids as a movement existed.

Congressional districts
Pennsylvania was divided into 11 districts, of which four were plural districts with 11 Representatives between them, with the remaining 7 Representatives elected from single-member districts. The districts were:
 * The PA's 1st congressional district (3 seats) consisted of Delaware and Philadelphia counties (including the City of Philadelphia)
 * The PA's 2nd congressional district (3 seats) consisted of Bucks, Luzerne, Montgomery, Northampton, Susquehanna, and Wayne Counties
 * The PA's 3rd congressional district (3 seats) consisted of Berks, Chester, and Lancaster Counties
 * The PA's 4th congressional district (2 seats) consisted of Cumberland, Dauphin, Huntingdon, and Mifflin Counties
 * The PA's 5th congressional district consisted of Bradford, Centre, Clearfield, Lycoming, McKean, Northumberland, Potter, and Tioga Counties
 * The PA's 6th congressional district consisted of Adams and York Counties
 * The PA's 7th congressional district consisted of Bedford and Franklin Counties
 * The PA's 8th congressional district consisted of Armstrong, Cambria, Indiana, Jefferson, Somerset, and Westmoreland Counties
 * The PA's 9th congressional district consisted of Fayette and Greene Counties
 * The PA's 10th congressional district consisted of Washington County
 * The PA's 11th congressional district consisted of Allegheny, Beaver, Butler, Crawford, Erie, Mercer, Venango, and Warren Counties

Note: Many of these counties covered much larger areas than they do today, having since been divided into smaller counties

Election results
Fifteen incumbents (14 Democratic-Republicans and 1 Federalist) ran for re-election, of whom ten were re-elected. The incumbents John Ross (DR) of the PA's 2nd congressional district, Robert Jenkins (F) of the PA's 3rd congressional district and Matthias Richards (DR) also of the 3rd district did not run for re-election. Two seats changed from Federalist to Democratic-Republican control and one seat changed from Democratic-Republican to Federalist control, for a net loss of 1 seat by the Federalists. In the 1st district, there was a split between three "New School" and one "Old School" Democratic-Republicans, which split the Democratic-Republican vote enough to allow one of the three seats in that district to be won by a Federalist.

Post-Election
All 18 Representatives elected in October appeared in Washington at the start of the 12th Congress. John Smilie (DR) of the PA's 9th congressional district died December 30, 1812. Abner Lacock (DR) of the PA's 11th congressional district resigned February 24, 1813, after being elected to the Senate. Both had been re-elected to the 13th Congress, and both districts were left vacant for the remainder of the 12th Congress.