Goforth was among the earliest settlers in Southwest Ohio, when he settled at Columbia, now a neighborhood of Cincinnati, in the Northwest Territory in early 1789. On January 4, 1790, Governor Arthur St. Clair established Hamilton County and named Goforth one of three Judges of the Court of Common Pleas and Justices of the Court of General Quarter Sessions of the Peace. Like other Democratic-Republicans in Ohio, statehood became important to William Goforth. To that end, he along with Thomas Goudy, David Zeigler, Robert McClure, Aaron Caldwell, William McMillan and Robert Benham formed a Committee of Correspondence in 1797 to share this desire with other counties in the Northwest Territory. He was elected one of the Hamilton County representatives in the Northwest Territory House of Representatives for the First Territorial Legislature, which met from September 16 to December 19, 1799 at Cincinnati, and from November 3 to December 9, 1800 at Chillicothe. On March 3, 1801, the Congress passed, titled "An Act giving a right of pre-emption to certain persons who have contracted with John Cleves Symmes, or his associates, for lands lying between the Miami rivers, in the territory of the United States northwest of the Ohio" Section 4 of this act called for the President to appoint two commissioners to "ascertain the rights of persons claiming the benefits of this act. Goforth and John Reily were named by the President to be these commissioners. In 1802, Goforth ran as a Democratic-Republican to be a delegate to the convention that would draft a constitution for the proposed state of Ohio. He was elected to the convention, which met from November 1 to November 29, 1802. He voted against ever allowing slavery in the state, and was in the minority in voting for suffrage and other civil rights for black people. After Ohio became a state, an election was held for Ohio's at-large congressional district in 1803. Goforth finished in fifth place. Either Goforth, or his son, also William was a Presidential elector in 1804, voting for Thomas Jefferson. Goforth died November 2, 1807 at Columbia. He was buried there, but re-interred at Spring Grove Cemetery. His tombstone reads: "Here rest the remains of Wm. Goforth who was born in Philadelphia, Pa., Apr. 1, 1731: Emigrated to Ohio in 1788: Assisted in forming her Constitution and was one of her first territorial judges: An officer in the Revolutionary War. He sacrificed everything for its success. He died Nov. 2, A.D. 1807 in the 76th year of his age."