Grant County is a county in the U.S. state of Nebraska. As of the 2020 United States Census, the population was 611, making it the fourth-least populous county in Nebraska and the ninth-least populous county in the United States. Its county seat is Hyannis. The county was founded in 1887 and named for Ulysses S. Grant, 18th President of the United States.

In 45 of the 50 states of the United States, the county is used for the level of local government immediately below the state itself. Louisiana uses parishes, and Alaska uses boroughs. In Connecticut, Massachusetts, and Rhode Island, some or all counties within states have no governments of their own; the counties continue to exist as legal entities, however, and are used by states for some administrative functions and by the United States Census bureau for statistical analysis. There are 3,242 counties and county equivalent administrative units in total, including the District of Columbia and 100 county-equivalents in the U.S. territories.