Erected on 12 Apr. 1911 as the Apostolic Vicariate of Northern Shensi, by division of the Apostolic Vicariate of Shensi, which on the same date took the name of Apostolic Vicariate of Central Shensi (v. SIAN), it received on 3 Dec. 1924 its present name of Y. and on 11 Apr. 1946 was elevated to a suffragan diocese of Sian. From the beginning it has been entrusted to the Friars Minor of the Province of Cantabria.
It has an area of about 50,000 sq. km. As of 30 June 1947, out of a total population of about 3,000,000, there were 9,500 Catholics; 19 Chinese and 17 Spanish priests; 2 foreign lay brothers; 7 major and 4 minor seminarians. The schools had already been suppressed for several years.
The evangelization of Y. began in the first decade of the present century. At the instigation of the Apostolic Vicariate of Northern Shensi (v. SIAN), Bishop Gabriel Maurice, O.F.M., between 1908 and 1911 founded several Christian communities in the mountainous region of the northern part of the vicariate, for whose better care the mission of Y. was erected. At the time of its foundation it had 2,000 faithful and 15,000 catechumens. From that year progress, despite difficulties of terrain and people, was notable, and in 1934 there were 9,515 baptized and 6,896 catechumens; but the following year the entire region fell under communist domination, which established their headquarters at Y., from which they have in recent times invaded the rest of Chinese territory.