The Teasdale name is almost certainly linked to the river Tees, which forms the boundary between the counties of Durham and Yorkshire. The river begins in the Northern Pennines, on the slopes of Cross Fell, near the Cumbrian border. After flowing east for eight kilometers it turns south east as far as Barnard Castle before winding south of Darlington and then out to sea just north of Middlesborough. The river flows through Upper and Lower Teesdale and has two spectacular waterfalls at High Force and Cauldron Snout.
It seems probable that several families took the name Teesdale (or one of the variants) at around the same time in the 16th century. There are early records of a Geoffrey de Tesdale at York in 1309, Alan de Tesdale at Marsfield in 1325, Walter de Tesdale at Jedburgh in 1298 and John Tesdall at Westminster in 1379. A high proportion of early surnames were derived from the place where the family had its main residence. It was common practice in the 12th and 13th centuries for the senior line of a land-owning family to adopt a hereditary surname of this type, while junior branches gradually acquired different surnames or variations as they moved around the British Isles. More research is needed before we can be confident about the early families.
River names in this area seem to be the oldest of place-names relating to the first Celtic settlers (long before the invasion of Angles, Saxons and Scandinavians). The river Tees was called “Tesa” in the Knytlinge Saga, a history of the Danish kings of the 10th and 11th centuries and later records have the name as Teisa and Taise. Place names in England are predominantly Anglo-Saxon or Norman in character with the exception of some natural features such as rivers, prominent hills and forests which require immediate identification in terms equally intelligent to natives and newcomers alike.
It is tempting to throw a bit of speculation into the pot of imagination and say the very early names in the International Genealogical Index (IGI) such as Tesdell, Tisdel, Tysdale or Tisdill could be derivatives of the early names for the river Tees. The family name could have evolved with the river. The IGI records for England clearly show a predominance of Teasdales followed by Teesdales and then much smaller groups of Tisdales, Teasdells, Teasdall and Tisdells. There are at least 45 variant names within the IGI and no doubt these variations are the result of the different local dialects in each county of England. The church authorities would transcribe the parish names as they were spoken by the migrant parishioners into the parish records and Bishops Transcripts.