The Clan/Sept History

The O'Neill family was quite prevalent in Irish history for almost 700 years, until the end of the 17th century. By the 14th century, it is thought that Ulster O'Neills numbered 29,000.
They are descendants of Niall of the Nine Hostages. After the death of King Niall Glúin Dubh (BlackKnee) in 919 AD, his grandson Domnall became the first to use and adopt the surname O'Neill.

The surname Niáll means champion. The surname O'Neill is derived from two Gaelic words, Uá Niáll, which means grandson of Niáll. It is also the surname of one of the three most important Gaelic families, the other two being, O'Brien and O'Conor.

The nickname creagh, derived from the Gaelic word craobh, meaning branch, was one by which earlier O'Neills were known. This nickname was given to them because they camouflaged themselves with greenery when battling against the Norsemen near Limerick.