It is now commonplace to see surnames written in the Irish language in Ireland, yet there is no online resource for checking the standard spelling and grammar of Irish-language surnames. We propose a data structure for handling Irish-language surnames which comprises bilingual (Irish–English) clusters of surname forms. We present the first open, data-driven linguistic database of common Irish-language surnames, containing 664 surname clusters, and a method for deriving Irish-language inflected forms. Unlike other Irish surname dictionaries, our aim is not to list variants or explain origins, but rather to provide standard Irish-language surname forms via the web for use in the educational, cultural, and public spheres, as well as in the library and information sciences. The database can be queried via a web application, and the dataset is available to download under an open licence. The web application uses a comprehensive list of surname forms for query expansion. We envisage the database being applied to name authority control in Irish libraries to provide for bilingual access points.