sidneySidney is a city in and the county seat of Richland County, Montana, United States, [4] less than 10 mi (16 km) west of the North Dakota border. The population was 6,346 at the 2020 census.With a vibrant downtown set against a beautiful oceanfront, Sidney is a popular tourist destination. It offers unique attractions, a number of quiet beaches, a range of shops, and excellent cafes and dining. Sidney also has a strong arts scene