Father Dunne wrote General Michael Corcoran requesting a recommendation for Colonel of the 90th Illinois. Corcoran recommended Timothy O'Meara, writing that he was "qualified in every respect to command the regiment now being raised under your auspices. He has had military experience ... he is also a Catholic---his name indicates his nationality."
Corcoran wrote Fr. Dunne that O'Meara "greatly distinguished himself" at the Battle of Ball's Bluff [as a captain in the 42nd NY] and that after being taken prisoner "he exhibited the sternest devotion to the cause of the Union, and was remarkable for the self-sacrificing spirit with which he endured his imprisonment." Corcoran also mentioned O'Meara's service in Juarez's army during the Mexican War of Reform, but did not mention, and may not have known about, O'Meara's previous service with the Regiment of Mounted Riflemen in the Southwest.
Born in Tipperary, O'Meara had immigrated with his family to New York before enlisting with the Mounted Rifles in 1855.
Col. Timothy O'Meara was mortally wounded during the fight at Missionary Ridge and died early the next morning, November 26, 1863.
After the war, when the members of the 90th Illinois held reunions, they met on the anniversary of the battle at the north end of Missionary Ridge. Not only had the regiment's colonel been killed, but the lieutenant colonel had been seriously wounded and the command structure had been decimated during that battle. On that day the Irishmen suffered 117 official casualties, while the unit's surgeon reported more than 140. Some of the "walking wounded" preferred to take the grueling hike up to Knoxville to relieve the Union troops under siege there rather than remain in the field hospital and be counted among the wounded.