Worth County is a county located in the northwestern portion of the U.S. state of Missouri. As of the 2020 census, the population was 1,973. It is the smallest county in the state in population and, excluding the independent city of St. Louis, the smallest in total area. Its county seat is Grant City. The county was organized February 8, 1861, and named for General William J. Worth, who served in the Mexican–American War. Worth County is also the youngest county in the state.

Grant City is a city in, and the county seat of, Worth County, Missouri, United States. The population was 817 at the 2020 census.