the county of tonnerre (latin "pagus tornodorensis") was east of auxerre and south of troyes, centred on the town of tonnerre in the yonne region of france. it was set up in the 8th century as a fiefdom of the bishops of langres, and first became centred on tonnerre in the 9th century. through marriage the family also gained the county of bar-sur-seine, although the tonnerre family then became extinct two generations later, with bar-sur-seine passing to the counts of brienne and the county of tonnerre passing to the dukes of nevers and auxerre.