Frontenac is a city in St. Louis County, Missouri, United States. The population was 3,612 at the 2020 census. The community name is inspired by the New France governor Louis de Buade de Frontenac. Benjamin and Lora Wood, who laid out the community's core called Frontenac Estates, that consisted of 26 two-acre estates, had made frequent trips to Quebec. The community was incorporated as 217 acres in 1947 and annexed another 967 acres in 1948.