Leonard is a city in Cass County, North Dakota, United States. The population was 248 at the 2020 census. Leonard was founded in 188…Leonard is a city in Cass County, North Dakota, United States. The population was 248 at the 2020 census. Leonard was founded in 1881. Leonard got its start in 1881 when the railroad was extended to that point. A post office has been in operation at Leonard since 1881.