Johann Leonhardt and his family are recorded on the 1798 census of Orlovskaya in Household No. Or57.
Nikolaus Leonhardt (age 2), son of Johann Leonhardt of Orlovskaya, and his mother (former wife of Johann Leonhardt) are recorded on the 1798 census of Ober-Monjou in Household No. Om75.
The death of Johann Leonhardt in 1821 is recorded on the 1834 census of Orlovskaya in Household No. 43.
- 1834 Orlovskaya Census (Household No. 43, 86).
- Mai, Brent Alan. 1798 Census of the German Colonies along the Volga: Economy, Population, and Agriculture (Lincoln, NE: American Historical Society of Germans from Russia, 1999): Om75, Or57.