Homer (Hal, too),
I see from Frederick Dyer's landmark "Compendium of the War of the Rebellion" vol. 2, pp. 1055 that the 25th Illinois Infantry Regiment was organized at St. Louis and mustered in on 4 August 1861. After a few more days in St. Louis the 25th went west along the existing length of the Pacific Railroad (terminus at Tipton, west Moniteau County, in 1861) with Union General Fremont's ponderous campaign against Springfield, MO between September and November. While in Jefferson City in late August, they MAY have met an up and coming U. S. Grant, who was there for a few days in August 1861 as a brand new brigadier general, as I recall my reading of "O.R." and his memoirs. There are two or three old (if we can call 20th century "old"} articles in the "Missouri Historical Review" of the State Historical Society of Missouri that deal with Fremont's very slow campaign that mentions the various Missouri towns they used (and perhaps Otterville).
I hope that helps.