In recognition of Illinois’ six regiments' service in the Mexican War, regimental numbers for infantry in the Civil War began at seven. * 7th Illinois Infantry Regiment * 8th Illinois Infantry Regiment * 9th Illinois Infantry Regiment * 10th Illinois Infantry Regiment * 11th Illinois Infantry Regiment * 12th Illinois Infantry Regiment * 13th Illinois Infantry Regiment * 14th Illinois Infantry Regiment * 15th Illinois Infantry Regiment * 16th Illinois Infantry Regiment * 17th Illinois Infantry Regiment * 18th Illinois Infantry Regiment * 19th Illinois Infantry Regiment * 20th Illinois Infantry Regiment * 21st Illinois Infantry Regiment * 22nd Illinois Infantry Regiment * 23rd Illinois Infantry Regiment * 24th Illinois Infantry Regiment * 25th Illinois Infantry Regiment *