Saline County was the site of fairly significant Civil War action, the so-called Battle of Marshall (although it was little more than a good-sized skirmish). The Battle of Marshall was the culmination of Colonel Jo Shelby's raid into Missouri during the fall of 1863, the main purposes of which were to recruit for the Confederacy, lift the spirits of Southern sympathizing people in Missouri, and perhaps occupy Federal forces that could otherwise be used in fighting battles in the East. After chasing Shelby for several days, General Egbert Brown finally caught up with the Rebels at Marshall and almost succeeded in trapping them in a deadly circle. Shelby was able to break through the Federal line, but his forces became separated into two bodies during the escape and both columns had to beat a hasty retreat toward the Arkansas border.
Probably the only other thing about Saline County that I'm familiar with at all is the fact that Arrow Rock, located on the river east of Marshall, was a significant town in the very early history of Missouri. For instance, it was the home of three Missouri governors: Claiborne F. Jackson, Meredith Miles Marmaduke, and John Sappington Marmaduke. It was also the home of artist George Caleb Bingham, who was famous for his paintings of Missouri scenes.