In 1812, after 406 years, the Moncada seignory ended, as the feudal constitution was abolished and Caltanissetta turned into the 22nd Comarca of Sicily. In 1819 it was declared capital of the province, but one year later it was sacked as a punishment for its loyalty to the House of Bourbon. In 1844 it was elevated to a bishopric seat.
After many Nisseni had taken part in his Mille's ("the Thousand's") deeds, Giuseppe Garibaldi entered the city, together with Cesare Abba and Alexandre Dumas, père. On October 22 of the same year a plebiscite declared Caltanissetta part of the new Kingdom of Italy.
After the unification of Italy was involved in a great economic boom largely due to intense mining of sulfur, but it was accompanied by various misfortunes: April 27, 1867 47 people died due to an explosion of fire damp in the mine of Trabonella, 65 miners died in November 12, 1881 in Gessolungo always an explosion, and another 51 in 1911 in Deliella and Trabonella.
In 1875, however, the population rose against the prefect, who was fired. On April 8, 1878, the city was connected to a railway, ending the historical difficulties in reaching it. Three years later the king Umberto I visited Caltanissetta along with his wife Margherita of Savoy and his son Victor Emmanuel III.
During the Second World War, as part of the Allied landing in Sicily, he suffered several bombings (July 1943) during which 351 civilians were killed. On July 10, U.S. troops landed in Gela a week before they entered and occupied the city
