Serving under Maj. Gen. Gordon Granger, the 77th Illinois Volunteers participated in the bloody initial phase of the Vicksburg Campaign, during which several days of futile Union attacks were launched before a protracted siege was made and won. After participating in the first Vicksburg battles, the 77th was part of the group of Union troops marched to the east, where on May 14, 1863, they took part in the Battle of Jackson, Mississippi, leading to the fall of that city.