In the Oxford Essential Reference Dictionary of the U. S. Military there is a question mark in reference to his birth as follows: (1740?-89).
Because research shows numerous conflicting sources with two different birth dates (1740 and 1753) and origin (Virginia and Georgia). Both have been included until additional information is found that proves or disproves one.
Questions have been raised in WikiTree forums previously: 
Certain sources state William Leigh Pierce is the child of Matthew and Elizabeth Pierce opposed to the parents that he is linked to on his profile.
A timeline has been created below so more details can be added about his early life when found in an effort to make conclusions on his date of birth.
1740: date of birth in Georgia supported by some sources including the Biographical Directory of the United States Congress.
1753: date of birth in Virginia supported by sources including New Georgia Encyclopedia.
1775: Returned in the summer to Williamsburg, Virginia to practice his skills after studying for a short time in Maryland under Charles Wilson Peale. In the autumn he participated in the fighting at Hampton, Virginia.
1776: On November 30th his was commissioned a Captain in Harrison's Continental Artillery Regiment (which became the First Continental Regiment of Artillery in 1779).
1778: His regiment was ordered to join the main army at Valley Forge, Pennsylvania in the spring.
1779: Pierce accepted a position as an aide-de-camp to General Sullivan resigning his former command as he was suffering from poor health. By summer, he travelled with Sullivan on an expedition to upstate New York to suppress the Iroquis who were loyal to the British.
1780: Returned to Williamsburg, Virginia on furlough and studied at the College of William and Mary becoming a member of Phi Beta Kappa.
1781: He accepted an invitation to serve at aide to Major General Nathanel Greene and joined him in February. In September, he fought in the Battle of Eutaw Springs near Charleston, South Carolina lead by Nathanael Greene. He was later presented by Congress with a ceremonial sword for his courage and bravery. (The account describes him as "young", he would have been about 28 if born in 1753 and about 41 if born in 1740).
1783: Left the army and established a import-export business with two fellow officers, Richard Call and Anthony Walton White, in Savannah, Georgia. Later that year, he married Charlotte Fenwick of South Carolina, the daughter of a wealthy planter.
1784: William and his wife moved to Savannah, Georgia where they acquired a house in town and the confiscated loyalist plantation of Belmont. He later sold his share of the business to partner Richard Call.
1785: Began a new business under the name William Pierce and Company.
1786: Elected to represent Chatham County in the Georgia State House of Representatives. He was then elected to the Continental Congress and became a delegate to the Constitutional Convention.
1787: He attended the Congress in New York City in January followed by the convention in Philadelphia, Pennsylvania in May. During this time he recorded a series of "Character Sketches" which would later be published in 1828 providing a contemporary narrative o the personalities of the founding fathers.
1789: William received a number of votes for governor but did not win the race. He died on December 10th at his plantation in Savannah, Georgia after an illness.
1790: His son William Leigh Pierce was born.
William Leigh Pierce, Georgia was an officer in the Revolutionary War (1775-1783), a member of the Continental Congress and a Georgia state legislator.
Although traditionally believed to be a native Georgian, Pierce was born in York County, Virginia, in 1753, the third and youngest son of Elizabeth and Matthew Pierce. Though frequently referred to with a middle name of "Leigh," he always signed his name as "William Pierce Jr.," perhaps to distinguish himself from an uncle of the same name.
During the Revolutionary War Pierce acted as an aide-de-camp to General Nathanael Greene and eventually attained the rank of brevet major. For his conduct at the battle of Eutaw Springs, Congress presented him with a ceremonial sword.
The year Pierce left the army, 1783, he married Charlotte Fenwick of South Carolina. They had two sons, one of whom died as a child. His son, William Leigh Pierce was born about 1789, and graduated from the College of New Jersey (now Princeton University) in 1808. He was the author of The Year, A Volume of Verse published in 1813.
Pierce made his home in Savannah, where he engaged in business. He first organized an import-export company, Pierce, White, and Call, in 1783, but it dissolved less than a year later. He made a new start with his wife's dowry and formed William Pierce & Company. In 1786 he was a member of the Georgia House of Representatives and was also elected to the Continental Congress.
At the Constitutional Convention Pierce did not play a large role, but he exerted some influence and participated in three debates. He argued for the election of one house of the federal legislature by the people and one house by the states; he favored a 3-year term instead of a 7-year term in the second house. Because he agreed that the Articles had been insufficient, he recommended strengthening the federal government at the expense of state privileges as long as state distinctions were not altogether destroyed. Pierce approved of the resulting Constitution, but he found it necessary to leave in the middle of the proceedings. A decline in the European rice market adversely affected his business. Soon after he returned to Savannah he went bankrupt, having "neither the skill of an experienced merchant nor any reserve capital." Only 2 years later, on December 10, 1789, Pierce died in Savannah at age 49 leaving tremendous debts.
Pierce's notes on the proceedings of the convention were published in the Savannah Georgian in 1828. In them he wrote incisive character sketches that are especially valuable for the information they provide about the lesser-known delegates.
Below is William Pierce's description of himself as well as his sketches of Benjamin Franklin and Alexander Hamilton:
My own character I shall not attempt to draw, but leave those who may choose to speculate on it, to consider it in any light that their fancy or imagination may depict. I am conscious of having discharged my duty as a Soldier through the course of the late revolution with honor and propriety; and my services in Congress and the Convention were bestowed with the best intention towards the interest of Georgia, and towards the general welfare of the Confederacy. I possess ambition, and it was that, and the flattering opinion which some of my Friends had of me, that gave me a seat in the wisest Council in the World, and furnished me with an opportunity of giving these short Sketches of the Characters who composed it.
Dr. Franklin is well known to be the greatest phylosopher of the present age; – all the operations of nature he seems to understand,- the very heavens obey him, and the Clouds yield up their Lightning to be imprisoned in his rod. But what claim he has to the politician, posterity must determine. It is certain that he does not shine much in public Council, – he is no Speaker, nor does he seem to let politics engage his attention. He is, however, a most extraordinary Man, and tells a story in a sty
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