Pennsylvania's Flag History
Pennsylvania's State Flag is composed of a blue field on which is embroidered the State Coat of Arms. The flag is flown from all state buildings, and further display on any public building within the Commonwealth is provided for by law. The first State Flag bearing the State Coat of Arms was authorized by the General Assembly in 1799. During the Civil War, many Pennsylvania regiments carried flags modeled after the U.S. Flag, but substituted Pennsylvania's Coat of Arms for the field of stars. An act of the General Assembly of June 13, 1907, standardized the flag and required that the blue field match the blue of Old Glory.
Pennsylvania's Coat of Arms, while not used in the same official capacity as the State Seal (although it contains the emblems of the seal), is perhaps a more familiar symbol of the Commonwealth of Pennsylvania. It appears on countless documents, letterheads and publications, and forms the design on Pennsylvania's State Flag. Provincial Pennsylvania's coat of arms was that of the Penn family. A state coat of arms first appeared on state paper money issued in 1777. This first coat of arms was nearly identical to the State Seal, without the inscription. In 1778, Caleb Lownes of Philadelphia prepared a coat of arms. Heraldic in design, it consisted of: a shield, which displayed the emblems of the State Seal --- the ship, plough and sheaves of wheat; an eagle for the crest; two black horses as supporters; and the motto "Virtue, Liberty and Independence." An olive branch and a cornstalk were crossed below the shield. Behind each horse was a stalk of corn, but these were omitted after 1805.
Numerous modifications were made to this coat of arms between 1778 and 1873, chiefly in the position and color of the supporting horses. In 1874, the legislature noted these variations and the lack of uniformity and appointed a commission to establish an official coat of arms for the Commonwealth. In 1875, the commission reported that it had adopted, almost unchanged, the coat of arms originally designed by Caleb Lownes ninety-six years earlier.
Link here to the Pennsylvania State Historical Society for facts, figures and history of Pennsylvania.