The ancient name for Tilliach „Cercinago“ indicates the population of the Tilliach area by the Romans. Ancient farmyard names of Roman source like Rals, Flatsch (Valatsch), Goll and Kosten sustain this knowledge. The village of Tilliach is first mentioned in a document that dates back to the second half of the 11th century. The historical tradition says that the area has originally been a Welsh horse pasture belonging to the farmers of Cadore, especially those in Comelico. The colonisation happened by the Bavarii around 600 AD, their traces can still be found in many farmyard names. In 769 AD the Anras mountain forms the border between the Slavic and the Bavarii settlement area. The upper Gailtal valley and the Kartitsch and Lesachtal valley where assigned to the Abbey of Innichen by duke Tassilo. The Bishopric of Brixen acquired the area of Obertilliach in 1075 AD by donations. This property was clearly amplified in the 13th century by the erection of farmyards on the sunny side of the valley. Around 1375 AD Silesian emigrants should have settled down, but there is no historic evidence for this. Documented are bloody conflicts between the inhabitants of Tilliach and those of the neighbouring Cadore. To reassess the border disputes with the Venetian Republic and the occupants of Cadore the new border was moved from Gail river to the Carnic Crest. In 1512 AD there was the last assault of Obertilliach.
In 1809 landlord Michl Weiler organized a rifleman division for the Tyrolean Rebellion against the French and the Bavarian. When the French General Ruska moved looting through Gailtal valley after the defeat in Lienz with 1.580 soldiers 1809, Ignaz Valiner (owner and first landlord of the Unterwöger) and his fellows opposed him. In 1852 the administrative district authority was established. From now on the village had a mayor, before there was a spokesperson or an administrator. Obertilliach belongs like all municipalities of East Tyrol to the district of Lienz.
The municipalities where allowed the self-administration and so they could democratically vote the municipal council and the mayor. In the war years from 1915 to 1918 Obertilliach had been in highest danger. Italian artillery fired at the village from mount Porze, but local riflemen could defend the village until the arrival or regular troops. At that time the inhabitants promised to commemorate every year the Friday in the week after the Feast of Corpus Christi, the so-called Feast of the Sacred Heart. This commemoration is held until today. By decision of the Tyrolean government on December 9, 1975 the municipality of Obertilliach was granted a municipal coat of arms. This coat of arms is divided obliquely and displays in the upper section the Brixen lamb and below a lion. The municipal coat of arms represents the judicial administration of Tilliach exercised by both the monastery of Brixen and the counts of Gorizia Tyrol (first mentioned in documents in the second half of the 11th century). This coat of arms was consigned to the municipality of Obertilliach in a ceremonial setting in occasion of the “Great Feast of the Sacred Heart” on June 25, 1976.