Idalia is an unincorporated community in Stoddard County, Missouri, United States. It is located six miles northeast of Dexter. A post offic…Idalia is an unincorporated community in Stoddard County, Missouri, United States. It is located six miles northeast of Dexter. A post office called Idalia was established in 1889, and remained in operation until 1966. According to tradition, the community was named after the daughter of the original owner of the site.