Site of the Confederate Invasion of Iowa, 12th Day of October, 1864. This monument marks the northern most point of incursion into Iowa by Confederate Forces. On October 12, 1864, Lieutenant James “Bill” Jackson led twelve heavily armed Missouri Partisan Rangers dressed in Union uniforms in a raid through Davis County, Iowa, resulting in the murder of three local citizens. • This Plaque Dedicated in 2005 • Davis County Civil War Guerrilla Raid Society.An associated plaque, installed by the SCV, makes the claim that: "Confederate Partisan Rangers came from Missouri to this point, the Furthermost North of any Confederate Incursion During the Civil War."
The incomparable Historical Marker Database records the Bloomfield marker at 40° 44.5′ N. The good folks near Salineville, Ohio have a marker, too. And though it's only as far north as 40° 37.228′ N, they claim the northernmost distinction as well. The Ohio marker reads:
Here, on July 26, 1863 occurred the northernmost engagement of Confederate forces during the Civil War. In this immediate area, troops under Major General John H. Morgan, C.S.A., and General James Shackelford, U.S.A., met in full engagement. After evading Union troops, Morgan’s forces were re-formed at Norristown, from whence they proceeded to West Point, where Morgan surrendered his command.I think you have to give the nod to Salineville, since Morgan's Raiders were full-fledged CSA units detached from a Confederate army before making their monumental raid. The Iowa incursion, by contrast, sounds more like a gang, even resorting to the use of disguise. We won't even entertain notions about the St. Albans, Vermont raid (bank robbers!), or naval actions.