George Grennell Jr. (December 25, 1786 – November 19, 1877) was a U.S. Congressman from Massachusetts. He was born in Greenfield, Massachusetts on December 25, 1786 to parents George and Lydia (Stevens) Grennell. He attended Deerfield Academy and graduated from Dartmouth College in 1808. He was admitted to the bar in 1811 and served as prosecuting attorney for Franklin County 1820–1828. Grennell served as a trustee of Amherst College 1838–1859, a judge of probate 1849–1853, clerk of Franklin County Courts 1853–1865, and the first president of the Troy and Greenfield Railroad.