Eldon is a city in Miller County, Missouri, United States, located 30 miles southwest of Jefferson City. The population was 4,416 as of the 202…Eldon is a city in Miller County, Missouri, United States, located 30 miles southwest of Jefferson City. The population was 4,416 as of the 2020 census. Eldon was platted in 1881, and according to tradition, named after a railroad official. A post office called Eldon has been in operation since 1881.