刘易斯县（Lewis and Clark County, Montana）是美国蒙大拿州中西部的一个县。面积9,059平方公里。根据美国2000年人口普查，共有人口55,716人。县治海伦娜 (Helena)也是州的首府。

成立于1865年2月2日，是该州最早成立的县之一。县名纪念以侦察密西西比河以西土地闻名的军人、探险家梅里韦瑟·刘易斯和威廉·克拉克。

Lewis and Clark County is a county located in the U.S. state of Montana. As of the 2010 census, the population was 63,395. Its county seat is Helena, the state capital. The numerical designation for Lewis and Clark County (used in the issuance of the state's license plates) is 5. The county was established in 1865 as Edgerton County, and was renamed "Lewis and Clark County" two years later. The present name was given in honor of explorers Lewis and Clark.