It has an area of 1,600 sq. km. with a population of 122,000 inhabitants, of whom 121,950 are Catholic. It has 30 parishes with 53 diocesan priests and 7 regular clergy, 1 seminary; 2 male religious communities and 20 female (1949).
The ancient see of the diocese was in Sulcis, today S. Antioco; it then passed to Tratales, where outside the Cathedral an inscription recalls the two bishops Alberto and Aimone (12th century). Pope Julius II transferred the diocese to I. on 8 December 1503, appointing Bishop G. Pilares; but in 1513 I. was united to Cagliari. Pope Clement XIII, by a bull of 18 March 1763, again separated I. from Cagliari, appointing Bishop L. Satta. The Cathedral, dedicated to St Clare of Assisi and begun at the close of the 13th century, was transformed internally with cross-vaulting during the Aragonese domination; other notable churches are the Gothic church of St Francis and that of the Maddalena di Valverde, known as the Capuchin church.