Carter County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 1,415, making it the seventh-least populous county in Montana. The county seat is Ekalaka.

Thomas Henry Carter was an American politician, who served as territorial delegate, a United States representative, and a U.S. Senator from Montana. Carter was born in Junior Furnace, Ohio, on October 30, 1854. Born to an Irish immigrant family, he spent most of his childhood in on small farms in the Midwest. In 1882, he moved to Helena, Montana to begin his law career there. He entered then politics, and was elected Montana's territorial delegate in 1888. Following Montana's admission into the union as a state, Carter represented the state in U.S. House of Representatives. He ran for re-election in 1890, but was narrowly defeated by Democrat William W. Dixon in the general election.