The 1st Ill. Cav., Col. Thos. A. Marshall, and fragments of Home Guard regiments in process of organization, were drawn back to Lexington, in face of the advance of Price's columns. There was also a mongrel field battery, consisting of one 4-pounder, three 6-pounders, one 12-pounder and two little 4-inch howitzers, the latter being useless on account of having no shells. The cavalry was only armed with pistols and sabers. No official Union reports are on file as to the affair, but the total strength of the garrison is given unofficially at from 2,640 to 3,300. The correspondent of the Missouri Republican gives these figures: 23d 111., Col. Mulligan............................... 800 Home Guards, Col. White.......................... 500 13th Mo., Col. Peabody................................ 840 1st Ill. Cav., CoL Marshall........................... 500 Total...................................................2,040 Col. Mulligan assumed command of the whole by seniority of commission. He was an Irishman with all his race's pugnacity, and also its effervescence. He was born in Utica, N. Y., in 1830, had graduated from a Roman Catholic college, studied law, and edited the principal Roman Catholic paper in the West, "The Tablet." 207 Lexington, which is the County seat of Lafayette County, was a very important place in frontier times, and the center of the great hemp-growing region of Missouri. It is situated on the south bank of the Missouri River, about 300 miles by its course above St. Louis, and about 84 miles below Kansas City by water, or 42 miles by rail. It consisted of two towns, Old and New Lexington, about a mile apart, having altogether about 5,000 people. It had some manufactories and two or three colleges, one of which, the Masonic College, situated on high ground between Old and New Lexington, a half mile from the river, was taken by Col. Mulligan for his position, which he proceeded to fortify with high, substantial works to accommodate 10,000 men, inclosing about 15 acres on the summit of the bluffs. Between 2,000 and 3,000 horses and other animals of the trains were gathered inside this inclosure. A week before Col. Mulligan's arrival, on Sept. 9, Gov. Jackson had briefly set up his Capital there, and held a session of that portion of the Legislature which adhered to him. The approach of Col. Pea-body caused a precipitate adjournment, and there was left behind $800,000 in coin, which was buried in the cellar of the college, with the great seal of the State of Missouri.