Reilly comes from an Irish surname meaning descendant of Raghallach.
Reilly comes from an Irish surname, most often linked to Ó Raghallaigh, meaning “descendant of Raghallach.” The underlying personal name is usually interpreted as conveying qualities like valiance or sociability, though early Gaelic names can be difficult to pin down with total certainty. Through anglicization, Ó Raghallaigh produced forms such as O’Reilly, Reilly, and Riley, which then took on lives of their own.
Reilly as a given name belongs to the modern wave of Irish surnames that migrated into first-name use, especially in the English-speaking world. Historically, the O’Reillys were a significant Gaelic family in what is now County Cavan, and the surname has deep roots in Irish political and regional history. Over time, related spellings entered broader public culture through immigration, literature, and popular entertainment.
In the United States, Riley became more common and eventually more gender-flexible, while Reilly retained a slightly more surname-like, distinctly Irish appearance. That spelling can signal heritage more overtly, preserving some of the family-name texture that smoother modern variants sometimes lose. The perception of Reilly has changed dramatically over the last century.
What once would have been recognized primarily as a surname is now heard as lively, friendly, and contemporary. It has the genial energy of many two-syllable Irish-derived names, but also a certain adaptability: athletic, literary, informal, even polished depending on context. Because of its kinship with Riley, Reilly participates in a broader naming trend toward surnames and gender-neutral sounds, yet it keeps a stronger sense of lineage. It feels modern without severing its roots, carrying with it the history of Gaelic family identity and the long journey of Irish names into global circulation.