Isaac Munroe St. John (November 19, 1827 – April 7, 1880) was a Confederate States Army brigadier general during the American Civil War.

[1][2][5] Isaac M. St. John began the Civil War as a private in the Fort Hill Guards of South Carolina in April 1861.

[1] By April 1862, he was Brigadier General John B. Magruder's chief engineer at Yorktown, Virginia, in the Peninsula Campaign with the rank of captain.

[1][6] In this position, he produced crucial ordnance supplies, including gunpowder and metals, for the Confederate Army, even as the Union blockade of Southern ports became increasingly effective.

[1][2] St. John resigned from the Nitre and Mining Bureau on January 31, 1864, because the Confederate Senate accused him of protecting draft dodgers.