William Allen (August 5, 1704 – September 6, 1780) was a wealthy merchant, attorney and chief justice of the Province of Pennsylvania, and mayor of Philadelphia during the colonial era.

A Loyalist, Allen agreed that the colonies should seek to redress their grievances with British Parliament through constitutional means, and he disapproved of the movement toward independence.

In 1720, he was admitted to the Middle Temple in London to study law, and at the same time became a pensioner at Clare College at the University of Cambridge.

In spring 1729, Allen was named alongside lawyer Andrew Hamilton, his future father-in-law, as a trustee for the purchase and building fund to develop the State House in Philadelphia, then the capital of the province.

By October 1730, Allen and Hamilton began to purchase lots on Chestnut Street at their own expense, the property on which the Pennsylvania State House, later known as Independence Hall, was built.

[4]: 89  By the will of Andrew Hamilton, dated July 31–August 1, 1741, Allen inherited all the land of the yard for the state house and its surrounding public grounds.

The following year, in 1736, he celebrated the opening of the nearly complete State House, later renamed Independence Hall, by hosting a feast for all residents and guests of the city; it was described at the time as "the most grand, the most elegant entertainment that has been made in these parts of America.

"[1] In 1739, when both Allen and Hamilton retired from the House, the opposition Quaker Party, unhappy with the Proprietors' paper money policies and the governor's support for war with Spain, regained control for the next seventeen years.

Allen lost his bid for a seat in 1740, and in 1742, the Quakers accused him of inciting sailors to riot during the Philadelphia election to intimidate their voters.

He established a £100 line of credit for West and, in a letter of introduction in 1760, called him "a young ingenious Painter of this City, who is desirous to improve himself in that Science, by visiting Florence and Rome.

Anne Allen married John Penn, a proprietor of the province with a one-fourth interest, who served as the last colonial governor of Pennsylvania.

On September 6, 1780, Allen died at home in the Mount Airy section of Philadelphia, at age 76, a year prior the end of the Revolutionary War in 1781.

Advertisements from The Pennsylvania Gazette in 1732 show that Allen and his business partner Joseph Turner participated in the slave trade.