In German "Ahn" means ancestor, as in ahnentafel (table of ancestors). This may indicate that the name is quite old.
My Ahn ancestors have been in Pennsylvania since at least 1806 when my great great grandfather Benjamin Franklin Ahn, Sr. was born, possibly in Willistown Township, Chester County. I have been unable to find his parents, but there are two other Ahn males, George and Samuel, in the same area who could be Benjamin's brothers.
My grandmother told me 25 years ago that her Ahn ancestors were French, but it's difficult at this distance in time to know if this was her wish or if there is any truth to the assertion. Perhaps they came from Alsace-Loraine.