The popular song, "I'll take you home again Kathleen" was written in 1876 and immortalized by singers Count John McCormack and Josef Locke. It is a song of longing for the land from whence the writer and his lady have come. The reference to "Across the ocean wide and wild" and "Where the fields are fresh and green" have generally both been taken to mean the Old Country, beloved original home of so many Irish immigrants to The United States of America.
But this is not necessarily the case.
The lyrics certainly point to Ireland as the "home" of the song, but not the antecedents of the composer. Thomas P Westendorf, was born in Virginia. Certainly many people of Irish descent were born on the east coast of the USA, but they would not bear the name Westendorf, which points to a more Germanic descent.
Also the song was written, not in Virginia, but in Plainfield, Ill. for his wife, who was not even named Kathleen, but Jennie, whilst she was visiting her home town of Ogdensburg, New York. So, perhaps the "home" referred to was not the Emerald Isle, at all, but the equally green fields of New York state. And what of the "ocean wide and wild". A bit more difficult to explain, but it probably refers to the prairies, which were, at that time, still as dangerous and as forbidding as any ocean.
At the time, the new "Oregon Trail" to the west coast was very well established. In the early days, the pioneers found the standard wagon, based on the solid Conestoga design favored by the other pioneers, too large and heavy when crossing the Rocky Mountains, killing even the sturdiest of ox teams long before the journey was completed. So a lighter version was developed by the Studebaker Brothers and nicknamed "Prairie Schooners".
Hence, by 1876, the concept of schooners – and thus the prairie being akin to a vast ocean – was firmly in the national lexicon, so it would be natural for Westendorf to incorporate references to a still largely untamed wild and wide ocean in his song, without meaning the Atlantic Ocean, across which lay a country of which he had scant knowledge.