MacManus, MacMaghnuis
A Gaelic surname meaning son of Manus (from Latin Magnus, great). A sept who were a branch of the Maguires, descenant of Maghnus, son of Donn Maguire, chief of Fermanagh who died in 1302. The chief of the sept lived at Senadh Mic Maghnusa now Belle Isle, in Lough Erne.
In 1890 McManus was numerous in Fermanagh. The estimated number of bearers was 6,182. In the United States McManus is the 1,478th most numerous surname with an estimated 22,000 bearers.