Ladue is an inner-ring suburb of St. Louis, located in St. Louis County, Missouri. As of the 2020 census, the city had a population of 8,989. L…Ladue is an inner-ring suburb of St. Louis, located in St. Louis County, Missouri. As of the 2020 census, the city had a population of 8,989. Ladue has the highest median household income of any city in Missouri with a population over 1,000.