Is Ireland in the British Isles? The Oxford English Dictionary seems clear. It tells us that the British Isles is:
1,750 more words
A group of islands, including Britain, Ireland (Northern Ireland and the Republic of Ireland), the Isle of Man, the Hebrides, the Orkney Islands, the Shetland Islands, the Isles of Scilly, and the Channel Islands, lying off the coast of northwestern Europe, from which they are separated by the North Sea and the English Channel.