Hazelnuts were first found in eastern and western Europe. Towards the end of the ice age, it expanded northwards and eastwards. Archaeological investigations of stone age sites have revealed the remains of hazelnut shells in now Germany, Scandinavia, and UK. There are also mentions of this nut in religious texts from the ancient civilizations of China.
Hazelnut is nothing but the ripe seeds of the woody shrubs bred by our ancestors. One of the first European hazelnut trees was brought to the US in the middle of the 19th century from central Europe.