The 9th Illinois was a 90-day regiment stationed at Cairo, IL to guard the crucial confluence of the Ohio and Mississippi rivers. General Prentiss, in charge of the area, appealed to his superiors for more troops; they were not available, troops in the region were needed to keep the peace in deeply divided Missouri. Prentiss was authorized to reorganize the regiments as three-year troops, if he could get the soldiers to volunteer for twelve times the time they’d originally signed on for.
The Regiment was mustered out of service on the 25th day of July, 1861. Because of the aspect of affairs in Missouri, but a small number of troops could be sent to Cairo, Ill., to take the place of the six regiments from Illinois, whose term of service was about to expire. Consequently an application was made by Gen. Prentiss to the Commander-in-chief, for permission to re-organize those six regiments in the field. This permission was granted; the re-organization of the several regiments was perfected, and the regiments recruited. The application made to the authorities for this permission was telegraphed, and granted in a dispatch from General Scott.