- Meagher County, Montana has 2,391.9 square miles of land area and is the 26th largest county in Montana by total area. Meagher County, Montana is bordered by Judith Basin County, Montana, Park County, Montana, Sweet Grass County, Montana, Cascade County, Montana, Gallatin County, Montana, Wheatland County, Montana, Lewis and Clark County, Montana, and Broadwater County, Montana.