Johnson County is a county in the U.S. state of Nebraska. As of the 2020 United States Census, the population was 5,290. Its county seat is Tecumseh. The county was formed in 1855, and was organized in 1857. It was named after Richard Mentor Johnson, who was Vice President of the United States from 1837 to 1841.

Tecumseh is a city in and the county seat of Johnson County, Nebraska, United States. The population was 1,677 at the 2010 census.