An Cnoc is the official Irish form of Knock, County Mayo, as established by order in Statutory Instrument No. 133 of 1975, An tOrdú Logainmneacha (Foirmeacha Gaeilge) (Uimhir 1)(Postbhailte), 1975.
The official Irish form, An Cnoc, was proposed by the Placenames Commission on the basis of collected evidence for the name in 1958. This form was published provisionally in Ainmneacha Gaeilge na mBailte Poist i gCúige Chonnacht, Liosta Sealadach (Oifig an tSoláthair, 1960) and comment was invited. It was ratified by the Commission and published in Ainmneacha Gaeilge na mBailte Poist (Oifig an tSoláthair, 1969).
The Commission is composed of recognised scholars in the fields of Irish toponomy and related disciplines representing various areas of the country. When the Irish form of Knock was examined in 1958, the Commission included several scholars who were well acquainted with the history and placenames of Connacht. In deciding on An Cnoc as the official form of the name, it is likely that the Commission was influenced by the fact that this was the traditional form used by native Irish speakers in east Mayo at the beginning of this century and saw no reason to change it.