Thomas Bonacum was an Irish-born American prelate of the Catholic Church. He was the first bishop of the Diocese of Lincoln in Nebraska, serving from 1887 until his death in 1911.

The Diocese of Lincoln is a Latin Church diocese in Nebraska, United States, and comprises the majority of the eastern and central portions of the state south of the Platte River. It is a suffragan see to the archdiocese of Omaha. The episcopal see is in Lincoln, Nebraska. Bishop James D. Conley is the current ordinary of the Diocese. The Cathedral of the Risen Christ is the cathedral parish of the diocese.