General Samuel Whiteside's militia brigade had been mustered into federal service at Rock Island under General Atkinson in late April, and divided into a scout or spy battalion commanded by James D. Henry, as well as four regiments (commanded by Colonels John DeWitt, Jacob Fry, John Thomas and Samuel M. Thompson), with judge William Thomas as their quartermaster. Atkinson had allowed Reynolds, Whiteside, and the militiamen to leave up the Rock River on April 27, while he brought up the rear with the regular soldiers, directing his least trained and disciplined men—to "move upon the Indians should they be within striking distance without waiting for my arrival". Governor Reynolds accompanied the expedition as a major general of militia.