The name "Tolmezzo" appeared for the first time in 1158 when Varnero of Carisarco and his wife Berta donate all their land "aput Tumech, vel alibi in Carnia” to the abbot of Moggio. The name of the town is traced back to the ancient name of the Tagliamento River that the Carni, the ancient inhabitants of the land, called Tulmetium. Later, the Ancient Romans named the river Tiliaventum, meaning "river of the linden trees" .
In 1258 the Patriarch Gregory of Montelongo granted to the community of Tolmezzo a number of privileges, including the right to hold a market. Il castello (h2) Si presume quindi che la struttura fortificata esistesse già nel XIII secolo e, verosimilmente, anche in quello precedente. Si trattava di un edificio maestoso, costruito in maniera esemplare da sofisticate maestranze. Che fosse una costruzione di prestigio lo attestano i numerosi frammenti di intonaco affrescato che doveva abbellire gli interni della torre.
Historians believe that the fortified structure already existed in the thirteenth century and maybe in the previous one. It was a majestic building, perfectly built by skilled workers as confirmed by the large number of painted plaster fragments found which probably decorated the interior of the tower.
The greatest period of the town of Tolmezzo and of Carnia, was the eighteenth century when, because of the lack of noble imposed by the Patriarca of Aquileia, the community of Carnia had already become a commercial society thanks to the creative and skilled Jacopo Linussio, a local entrepreneur that started a factory of fabrics employing more than 35,000 workers: at that time it was the biggest factory all over Europe.
Today the clothes and fabrics produced in the old factory, along with many other items of Carnic traditional craftsmanship, are kept in the Museo Carnico of Folk Arts "Michele Gortani" in the centre of Tolmezzo.
During World War I, Tolmezzo hosted the military command of the "Zona Carnia", and became, for lots of Italian soldiers, the last stop before the forefront on the "Mount Pal Piccolo" and the "Mount Pal Grande". Two military hospitals were set up here, and until 1917 the town was the operational centre in the Carnia's second line.
Nowadays the town has a population of 10,577 inhabitants, but, being the most important centre of Carnia, it provides facilities to all the mountain territory, including the cinema, the theatre, the auditorium with 492 seats, the hospital, a large number of schools, shops and restaurants and a lot of sports facilities including: