Historically, the name "St George's Channel" was used interchangeably with "Irish Sea" or "Irish Channel" to encompass all the waters between Ireland to the west and Wales to the east. Some geographers restricted it to the portion separating Wales from Leinster, sometimes extending south to the waters between the West Country of England and East Munster; the latter have since the 1970s come to be called the Celtic Sea. In Ireland "St George's Channel" is now usually taken to refer only to the narrowest part of the channel, between Carnsore Point in Wexford and St David's Head in Pembrokeshire. However, it remains common in Ireland to talk about a cross-channel trip, cross-channel soccer, etc., where "cross-channel" means "to/from Great Britain".
The current (third, 1953) edition of the International Hydrographic Organization's publication Limits of Oceans and Seas defines the southern limit of "Irish Sea and St. George's Channel" as "A line joining St. David's Head ( ) to Carnsore Point ( )"; it does not define the two waterbodies separately. The 2002 draft fourth edition omits the "and St. George's Channel" part of the label.
A 2004 letter from the St.George's Channel Shipping Company to Seascapes, an RTÉ Radio programme, said that St George's Channel bordered the Irish coast between Howth Head and Kilmore Quay, and criticised contributors to the programme who had used "Irish Sea" for these waters.
The name "St George's Channel" is recorded in 1578 in Martin Frobisher's record of his second voyage. It is said to derive from a legend that Saint George had voyaged to Roman Britain from the Byzantine Empire, approaching Britain via the channel that bears his name. The name was popularised by English settlers in Ireland after the Plantations.
- "Muir Bhreatan". logainm.ie. Placenames Branch (Department of Community, Equality and Gaeltacht Affairs). Retrieved 18 September 2010.
- C.Michael Hogan. 2011. Irish Sea. eds P.Saundry & C.Cleveland. encyclopedia of Earth. National Council for Science and the Environment. Washington DC
- Andrews, John Harwood (January 1997). Shapes of Ireland: maps and their makers 1564–1839. Geography Publications. pp. 87–88, 155. ISBN 978-0-906602-95-9. Retrieved 18 September 2010.
- Thomas Curtis, ed. (1839). "George's Channel (St.)". The London encyclopaedia. Vol. 10. p. 133. Retrieved 18 September 2010.
- Heslinga, Marcus Willem (1979). The Irish border as a cultural divide: a contribution to the study of regionalism in the British Isles. Van Gorcum. p. 8. ISBN 978-90-232-0864-8. Retrieved 18 September 2010.
- "Corrections to pages 12 and 13" (PDF). Limits of Oceans and Seas, 3rd edition. International Hydrographic Organization. 1953. Retrieved 28 December 2020.
- Choo, Sungjae (2007). "The Cases of International Standardization of Sea Names and Their Implications for Justifying the Name East Sea" (PDF). Journal of the Korean Geographical Society. 42 (5): 751, Table 3, footnote. Retrieved 15 August 2012.
- "2002 Draft of Limits of Oceans and Seas". IHO. Retrieved 25 May 2016.
- "Seascapes News Summary". RTÉ.ie. 30 September 2004. Archived from the original on 25 May 2012. Retrieved 18 September 2010.
- Taylor, Isaac (1896). "St. George's Channel". Names and their histories, alphabetically arranged as a handbook of historical geography and topographical nomenclature. Rivington, Percival. p. 243. Retrieved 18 September 2010.
- Room, Adrian (2006). "St George's Channel". Placenames of the world: origins and meanings of the names for 6,600 countries, cities, territories, natural features, and historic sites. McFarland. p. 326. ISBN 978-0-7864-2248-7. Retrieved 18 September 2010.