Saint Onge is an unincorporated community and census-designated place in Lawrence County, South Dakota, United States. As of the 2020 census, the population was 170. Saint Onge was laid out in 1881. The community was named for Henry St. Onge, a pioneer settler. A post office called Saint Onge has been in operation since 1881. Saint Onge has been assign…Saint Onge is an unincorporated community and census-designated place in Lawrence County, South Dakota, United States. As of the 2020 census, the population was 170. Saint Onge was laid out in 1881. The community was named for Henry St. Onge, a pioneer settler. A post office called Saint Onge has been in operation since 1881. Saint Onge has been assigned the ZIP code of 57779.