Tucker was never mustered into the Union Army, remaining a colonel in the Illinois militia during the term of his service in the Civil War.

[16] State militia troops called the Mechanics Fusileers, who were apprentice and journeyman carpenters, built the barracks in October and November 1861.

He had to use increasingly hard measures to curb considerable drunk and disorderly conduct by recruits in camp and in the city of Chicago, where the soldiers abused pass privileges.

[19] On February 16, 1862, the Union Army under then Brigadier General Ulysses S. Grant captured Fort Donelson on the Cumberland River near Dover, Tennessee[20] and with it about 12,000 to 15,000 Confederate prisoners.

[21] The army was unprepared to handle this large group of prisoners and scrambled to find places to house them.

[23] They were housed for their first few days at the camp in the White Oak Square section along with newly–trained Union soldiers about to depart for service at the front.

[25] On February 23, 1862, the Union troops vacated the camp except for an inadequate force of about 40 officers and 469 enlisted men left to guard the prisoners.

[31] The first group of prisoners was treated reasonably well under the circumstances and despite the inadequacy of the grounds, barracks and sewer and water systems, they were given clothing and enough to eat, although not a balanced diet.

[37] Some escapes were aided by Southern sympathizers in Chicago and others were facilitated by lax administration by Colonel Mulligan and the guards.

[37] Even though he remained in the Illinois militia and was not taken into federal service, Colonel Tucker returned to command the camp on June 19, 1862.

[38] To deal with local civilian sympathizers who might be aiding escapes, Colonel Tucker declared martial law on July 12, 1862.

[41] In the summer of 1862, Henry Whitney Bellows, president of the U.S. Sanitary Commission,[42] wrote the following to Lieutenant Colonel William Hoffman, Union Army commissary general of prisoners, who had considerable authority over Union prison camps,[43][44] after visiting the camp: "Sir, the amount of standing water, unpoliced grounds, of foul sinks, of unventilated and crowded barracks, of general disorder, of soil reeking miasmatic accretions, of rotten bones and emptying of camp kettles, is enough to drive a sanitarian to despair.

I do not believe that any amount of drainage would purge that soil loaded with accumulated filth or those barracks fetid with two stories of vermin and animal exhalations.

[50] Through September 1862, 980 Confederate prisoners and 240 Union Army trainees and guards had died at Camp Douglas, almost all from disease.

[54] Under Tyler's command these Union soldiers had to live under similar conditions to those endured by the Confederate prisoners from Fort Donelson.

By November, forty soldiers of the 126th New York Volunteer Infantry Regiment were dead and about another sixty were ill with fevers.