Islam can be found in the old world and the new.
Muslims came to the New World at pretty much the same time as Columbus (some of his captains and other crew may have been Muslims) and possibly well before. Indeed Muslims of many ethnicities have been in the Americas for centuries.
But the heartland of Islam has always been the heartland of humanity. That is, the central or middle parts of the world—with Arabia being the home of the Prophet Muhammad. Today the predominantly Muslim countries range from Morocco in the West and from there moving eastward through North and West Africa to Arabia, then continuing through Central Asia to the Indian Sub-continent and finally to the East Indies.