Isaac Thom was born in Windham on March 1, 1746 to parents, William Thom and Elizabeth Weir Thom. They emigrated to America from Londonderry, Ireland in 1736; they settled in Windham that same year. Isaac was born and raised upon the family farm at the north end of Cobbett's Pond; the farm William had purchased in 1743. In 1769 Dr. Isaac Thom began practicing medicine, and quickly became very successful as the first regular physician in Windham. That same year he married Persis Sargent of Methuen, MA; together the couple had twelve children, half of which were born in Windham and the other half of which were born in Londonderry. For the thirteen years that he practiced medicine in Windham, he is recorded as having been highly esteemed by all who knew him. Thom was a prominent and influential figure in town, presiding over town meetings and serving as a selectman for brief periods during the 1770s. He was also a member of the committee of safety during the American Revolutionary War. Such committees were formed to "keep watch of and act upon events pertaining to the public welfare." The committees often also had control of the local militia. In 1782 he moved from Windham to Londonderry, purchasing a property that is now in Derry. He continued practicing medicine for over a decade, retiring from his long career in 1795. While a resident of Londonderry, Thom served as the town's postmaster and justice of the peace for several years. Isaac Thom passed away on July 13, 1825, surviving his wife by only a few years.
1805 document signed by Isaac Thom as justice of the peace of Londonderry