John Martin Henni (June 15, 1805 – September 7, 1881) was a Swiss-born Catholic prelate who served as the first Archbishop of Milwaukee from 1843 until his death in 1881.

John Henni was born on June 15, 1805, in the village of Misanenga, municipality of Obersaxen, in the canton of Graubünden in Switzerland.

While Henni was in Rome, he was recruited by Bishop Edward Fenwick to complete his seminary studies in the United States and be ordained for the Diocese of Cincinnati.

After arriving in Baltimore, Maryland, in 1829, Henni traveled to Bardstown, Kentucky, to complete his studies at Saint Thomas Seminary.

[2] The diocese in 1830 transferred Henni to Canton, Ohio, to serve as pastor of St. John parish, along with several mission churches in the region.

At the meeting, he proposed the establishment of a seminary to prepare priests to minister to the large German immigrant population in the United States.

[2] On November 28, 1843, Henni was appointed the first bishop of the newly erected Diocese of Milwaukee by Pope Gregory XVI.

Henni received his episcopal consecration on March 19, 1844, from Purcell, with Bishops Michael O'Connor and Richard Pius Miles serving as co-consecrators.

At the time of Henni's consecration, the City of Milwaukee had one church; the diocese contained five priests to serve 5,000 Catholics.