On December 20, 1774, Montgomery is nominated to the Chester County Committee of Inspection to enforce the trade boycott established by the First Continental Congress. The following month, he is nominated as a Chester County delegate to the Convention for the Province of Pennsylvania (January 23–28, 1775) where they pass 27 resolutions to "restore harmony with Great Britain" while logistically preparing for war. Eighty-six days later, the "shot heard round the world" ignites the American Revolutionary War and Siege of Boston. On June 30, 1775 the Pennsylvania Committee of Safety was established, essentially displacing the governing Provincial Assembly until the Pennsylvania Constitution of 1776, and William was re-commissioned a colonel in command of the 4th [Elk] Battalion, comprising 450 infantry in eight companies. In February 1776, the Chester County Committee of Inspection tasked Montgomery, along with two others, with safeguarding the county's gunpowder magazine.