Native immediately west of the Rockies. Introduced to California and Eurasia. The species is now the "most widespread alien crayfish in Europe, occurring in 25 countries, from Finland to Great Britain and from Spain to Greece. It was first introduced to Great Britain in 1976 and is now widespread across the British mainland as far north as the Moray Firth. It has also been observed on the Isle of Man, but not in Ireland.[9] Ireland is the last European country having no alien crayfish." (Wikipedia)