The Counties of Meath and Westmeath Act 1543 proclaimed Westmeath a county, separating it from Meath. Mullingar became the administrative centre for County Westmeath. The town was originally named Maelblatha, and takes its modern name from a mill noted in the legend of Colman of Mullingar.
Traditionally a market town serving the large agricultural hinterland, Mullingar remains a significant commercial location. It had a tradition of cattle-trading until 2003 when its cattle market was closed for development of a mixed commercial and residential scheme called Market Point. However, in 2014 the local County Council have allowed an annual Christmas Market to take place on Mount Street.
Mullingar has a number of neighbouring lakes, including Lough Owel, Lough Ennell and Lough Derravaragh. Lough Derravaragh is also known for its connection with the Irish legend of the Children of Lir. The town of Mullingar is linked to Lough Ennell via Lacy’s Canal and the River Brosna. Another nearby waterway is the Royal Canal, which loops around Mullingar.