Westmeath's principal rivers are the Shannon and the Brosna, and numerous lakes, or loughs, are in the county, the largest of which is Lough Ree.

Agriculture is the chief occupation of the inhabitants. Several limestone quarries are here, as well as factories engaged in the manufacture of textiles, most notably wool tweed, cotton and linen goods.

Situated on Ireland's central plain, the county is mostly flat with a high point of 276 m (906 ft). Westmeath formed part of the ancient kingdom of Meath and became an independent county in 1541.