Illinois City is just upstream from Muscatine, Iowa. Access to the lock and dam is off of IL-92 on the east side of the river. The main structure consists of 4 large roller gates and 15 smaller Tainter gates. The lock is the standard 600 feet long by 110 feet wide upper Mississippi River lock. The structure also includes an uncompleted auxiliary lock, as do most of the Mississippi River lock structures.

The large concrete dam structure blocks the main channel of the Mississippi River, and connects from the Illinois side to Hog Island. A earthen dike and overflow spillway crosses the remainder of the river from Hog Island to the City of Muscatine, Iowa.