William Grymes Pettus (1794–1867) was a Missouri politician.

William Grymes Pettus was born in Mecklenburg County, Virginia on December 31, 1794.

While a United States General Land Office clerk in St. Louis, he was elected secretary of the State Convention which wrote the Missouri Constitution when it was admitted into the United States in 1821.

[1] His public service included Secretary of State in the Alexander McNair administration, Probate Judge of St. Louis County, and in 1832 he was elected a member of the Missouri Senate for the St. Charles District.

[1][2] He married Caroline R. Morrison on December 31, 1826.