The Clan/Sept History

There are many Irish surnames being used today in forms that are quite different
than their original, ancient forms. MacManus originally appeared in Gaelic as
Mac Maghnuis, which means son of Manus. The personal name Manus, imported into
Ireland by the Norse, is ultimately derived from the Latin forename Magnus.

Irish names were rarely spelled consistently in the Middle Ages. Spelling
variations of the name MacManus dating from that time include MacManus,
MacManners, McManus, Manus and others.
First found in county of Roscommon, where they held a family seat from ancient
times.
Thousands of Irish Families left for North American shores in the 19th century.
These people were searching for a life unencumbered with poverty, hunger, and
racial discrimination. Many arrived to eventually find such conditions, but many
others simply did not arrive: victims of the diseased, overcrowded ships in
which they traveled to the New World. Those who lived to see North American
shores were instrumental in the development of the growing nations of Canada and
the United States. A thorough examination of passenger and immigration lists has
disclosed evidence of many early immigrants of the name MacManus: Bessie
McManners settled in Boston in 1847; Bernard McMannis settled in Philadelphia in
1828; Andrew, Hugh, Patrick, Terrence McMannus all arrived in Philadelphia
between 1840 and 1860.