Short answers, pulled from the story.
The Army of the Potomac was created in July 1861 shortly after the First Battle of Bull Run. Major General George B. McClellan formed the army on the 26th of July 1861 from forces in former Departments of Northeastern Virginia, Washington, Pennsylvania, and the Shenandoah.
Major General George Meade was appointed commander of the Army of the Potomac on the 28th of June 1863 just three days before the battle began. Ulysses S. Grant located his headquarters with the army from May 1864 to April 1865 while Meade retained command of the force.
The Army of the Potomac recruited soldiers from Northern cities such as New York City, Philadelphia, and New Jersey. These men included both native and foreign-born populations including a significant Irish immigrant population that rose throughout the mid 19th century.
The Army of the Potomac disbanded on the 28th of June 1865 shortly following participation in the Grand Review of Armies. Eight corps served in the army during 1863 but reorganization left only four corps by March 1864 due to attrition and transfers.
The army originally consisted of fifteen divisions plus an Artillery Reserve and Cavalry Command. Edwin V. Sumner commanded one division while William B. Franklin led another and Louis Blenker commanded a third division until Nathaniel P. Banks took over that unit.