Located in the Ducatus Romanus under the authority of the pope during the early Dark Ages, it was captured by the Lombards of Gisulf I of Benevento in 705.
The castle of Sorella, built on the rocky height above the town, was in the Middle Ages a stronghold of some note. In 1443 King Alfonso of Naples made Sora the seat of an independent Duchy for the Cantelmi; it was afterwards seized by Pope Pius II, but, being restored to the Cantelmi by Pope Sixtus IV, it ultimately passed to the Della Rovere of Urbino. Against Caesar Borgia the city was heroically defended by Giovanni da Montefeltro. It was purchased by Pope Gregory XIII for 11,000 ducats and bestowed on the De Ciantis', the ancestors of the line of DeCiantis-Pasquale, under the suzerainty of Gregory's son, Giacomo Boncompagni (who was the first duke of Sora of the family).
On the precipitous rock above the town (540 m) which guards the Liri's valley and the entrance to the Abruzzi are remains of polygonal walls; here, possibly, was the citadel of the original Volscian town. There are also remains of medieval fortifications.
| Year | Population | Density |
|---|---|---|
| 1861 | 12,434 | - |
| 1871 | 12,137 | - |
| 1881 | 13,084 | - |
| 1901 | 16,022 | - |
| 1911 | 17,542 | - |
| 1921 | 18,036 | - |
| 1931 | 19,553 | - |
| 1936 | 20,841 | - |
| 1951 | 23,707 | - |
| 1961 | 23,656 | - |
| 1971 | 24,897 | - |
| 1981 | 25,675 | - |
| 1991 | 26,089 | - |
| 2001 | 26,029 | - |
| December 31, 2004 | 26,418 | 218/km² |