From the NE edge of Maine (nearest bit of USA) to the nearest bit of Eire, is about 2600 miles (4180 km). If you mean from centre of USA to centre of Ireland, you're looking at a distance of (roughly) 6759 km (4200 miles).
You can play for yourself, finding out how far away the rest of the world is, if you download a copy of Google Earth.
You can play for yourself, finding out how far away the rest of the world is, if you download a copy of Google Earth.