McPherson County is a county in the U.S. state of Nebraska. As of the 2020 Census, the population was 399, making it the least populous county in the state of Nebraska and the fifth-least populous county in the United States. Its county seat is Tryon. The county was formed in 1890 from Logan County; it was named for American Civil War General James B. McPherson. In 1913, a portion of McPherson County was partitioned off to create Arthur County, giving McPherson County its present boundaries.