It has an area of 19,155 sq. km. with a population of 3,316,865, of whom 1,320,624 are Catholics, distributed in 754 parishes, served by 1,026 diocesan priests and 264 regular clergy; it has two seminaries, one in R. and the other in Mergentheim; 30 male and 24 female religious communities (Ann. Pont. 1952, p. 342). The diocese is a suffragan of Freiburg im Breisgau.
Due to the secularization of 1803, Württemberg, hitherto entirely Protestant, acquired Catholic territories, administered by the dioceses of Constance, Augsburg, Würzburg, Worms, Speyer, and the provostship of Ellwangen. To simplify this situation, the government for Württemberg territories established a general vicariate at Ellwangen, with a seminary and theological faculty. The general vicar became the auxiliary bishop of Augsburg, previously provost of Ellwangen, Franz Karl Fürst von Hohenlohe. His appointment was not initially regular from the ecclesiastical point of view; only later did he receive confirmation from the primate V. Dahlberg. The Holy See, however, only in 1816 recognized the general vicariate and appointed Rev. von Keller as pro-vicar, with the right of succession. In 1817, the remaining Württemberg territories not yet dependent on the new vicariate were added to II. In the same year, the seat of the vicariate was transferred to R., and the theological faculty was moved to Tübingen. The bulls Provida sollersque of 16 Aug. 1821 and Ad Dominici gregis of 11 Apr. 1827 then established the diocese, determining the rights of the bishop and those of the Chapter. The first bishop became the same general vicar von Keller (1828-45), followed by Joseph Lipp, parish priest of Ehingen. Religious life saw notable growth through popular missions and charitable works. Under Karl Joseph von Hefele (1860-93), while the Kulturkampf raged throughout Germany, the diocese was almost untouched by II. Bishop Wilhelm von Reiser (1803-98) distinguished himself by his care for Catholics in the predominantly Protestant areas of the diocese (diaspora). Bishop Wilhelm von Keppler (1808-1926) is known for his oratory and for his work restoring the monasteries of Neresheim and Weingarten. Bishop J. B. Sproll (1927-49) fought against the errors of Nazism and had to live in exile for six years.
The diocese has 1,089 churches, 744 parishes, 1,026 diocesan priests; of the 3,317,000 inhabitants, 1,302,000 are Catholics.