Republic is a city in Christian and Greene counties in the U.S. state of Missouri. As of the 2020 census, the city's population was 18,750. In …Republic is a city in Christian and Greene counties in the U.S. state of Missouri. As of the 2020 census, the city's population was 18,750. In 2019, its population was 16,938, making it the second largest city in Greene County in the U.S. state of Missouri. It is also the fourth largest city in the Springfield, Missouri, Metropolitan Statistical Area.