The state of Montana has a total of 56 counties. Beaverhead County is the oldest (founded in 1864) while Petroleum County is the youngest (established in 1926).

Yellowstone County is the most populous, with a population of 155,634. Beaverhead County has the most land area (14,356 km2), while Silver Bow County has the smallest (1,860 km2).

Please find a list of all Montana counties arranged alphabetically below.

• Beaverhead County, MT
• Big Horn County, MT
• Blaine County, MT
• Broadwater County, MT
• Carbon County, MT
• Carter County, MT
• Cascade County, MT
• Chouteau County, MT
• Custer County, MT
• Daniels County, MT
• Dawson County, MT
• Deer Lodge County, MT
• Fallon County, MT
• Fergus County, MT
• Flathead County, MT
• Gallatin County, MT
• Garfield County, MT
• Glacier County, MT
• Golden Valley County, MT
• Granite County, MT
• Hill County, MT
• Jefferson County, MT
• Judith Basin County, MT
• Lake County, MT
• Lewis and Clark County, MT
• Liberty County, MT
• Lincoln County, MT
• Madison County, MT
• McCone County, MT
• Meagher County, MT
• Mineral County, MT
• Missoula County, MT
• Musselshell County, MT
• Park County, MT
• Petroleum County, MT
• Phillips County, MT
• Pondera County, MT
• Powder River County, MT
• Powell County, MT
• Prairie County, MT
• Ravalli County, MT
• Richland County, MT
• Roosevelt County, MT
• Rosebud County, MT
• Sanders County, MT
• Sheridan County, MT
• Silver Bow County, MT
• Stillwater County, MT
• Sweet Grass County, MT
• Teton County, MT
• Toole County, MT
• Treasure County, MT
• Valley County, MT
• Wheatland County, MT
• Wibaux County, MT
• Yellowstone County, MT