Poplar Bluff is a city in Butler County in southeastern Missouri, United States. It is the county seat of Butler County and is known as "The G…Poplar Bluff is a city in Butler County in southeastern Missouri, United States. It is the county seat of Butler County and is known as "The Gateway to the Ozarks" among other names. The population was 16,225 at the 2020 census. The Poplar Bluff Micropolitan Statistical Area consists of all of Butler County. The city is at the crossroads of U.S. Route 60 and U.S. Route 67.