The billhook is known and used in the Baltic States of Estonia, Latvia and Lithuania as well as the neighbouring countries of Finland, Belarus, Russia and Poland.
A 'kiin' from Estonia, with its curved blade and socketted handle it has many similarities with billhooks from central and southern Europe (from the Eesti Ravha Museum collection).
With an eye for an axe handle this version is similar to those from Russia, and has probably been taken to the USA by immigrants where it has been developed into the American bush hook, or brush axe.
Found in North Yorkshire (ref LANCUM-08AF65) this would appear to be Estonian in origin. From an 8th to 9th century site, it would appear to be evidence of medieval trading links between the Baltic and Anglos Saxon England.
I am indebted to Mart Reino, an Estonian blacksmith, who kindly sent me the information on Estonian billhooks, and a link to the Estonian Museums Public Portal from where I obtained most of the above images.