In 1745 during King George's War (1745–1748), he was put in charge of building and defending Fort Massachusetts and the line of defences in western Connecticut and Massachusetts. He was absent when the fort was taken and destroyed by the French in August 1746. After the war ended, Williams spent considerable effort urging the settlement of new townships in the western portion of Massachusetts along the Hoosac River at the end of the 1740s. Many of the early settlers in this region were soldiers stationed at Fort Massachusetts during the war, including Williams himself.