Y DNA reveals four distinct male lines that are related only by surname. People within each group share a common male ancestor but the groups do not share a common male ancestor: Group 1: The Stradbally Cosby Family. This family documents back to Francis Cosby (1510-1580) and are associated with Stradbally Hall, county Laois, Ireland. There are no Y-DNA matches of anyone from North America to this group. Group 2: The Cosby/Cozby/McCloskey Group. This group includes the male descendants of George Cosby (c. 1759-1806) who has been in Canada since 1784 and a line descended from John Cozby (c. 1713-1793) and Elizabeth Trimble who established a family in North and South Carolina. These two lines share a distant common male ancestor that descend from Niall Noígíallach aka Niall of the Nine Hostages who is the ancestor of the Uí Néill dynasties that dominated Ireland from the 6th to the 10th centuries. His son, Eogain established the kingdom of Ulster. This line is being researched by the Cenél nEógain (kindred of Eoghan) Project at this link: https://www.familytreedna.com/groups/cenel-eoghainy-dnaproject/about/background . The closest current day family association is with the McCloskey sept from County Derry and is associated with the Dungiven area. Group 3: The colonial Cosbys of Virginia. This group includes descendants of John Cosby who died 1695 in Hampton Parish, York County, Virginia. His origins are unknown. Y DNA confirms there is no connection to the Stradbally Cosby family on the male line. Group 4: The Cosbeys of Northern Ireland. This line has been in Ireland for at least five generations. Autosomal DNA results reveal cousin relationships between the different COSBY Y-DNA lines. Additional information is available at this link: http://one-name.org/name_profile/Cosby/