Hull BB-65 was originally to be the first ship of the s, but changes during the Second World War resulted in her being reordered as an midway through the war. Adherence to the Iowa-class layout rather than the Montana-class layout allowed BB-65 to gain eight knots in speed, carry more 20 mm and 40 mm anti-aircraft guns, and transit the locks of the Panama Canal; however, the move away from the Montana-class layout left BB-65 with a reduction in the heavier armaments and without the additional armor that were to have been added to BB-65 during her time on the drawing board as USS Montana.
Like her sister ship , Illinois was still under construction at the end of World War II. Her construction was canceled in August 1945, but her hull remained until 1958 when it was broken up.
Originally, BB-65 was to be the United States Navy's counter to the Empire of Japan's s, whose construction at the time was known to the highest ranking members of the United States Navy, along with the rumors that Yamato and Musashi were carrying guns of up to . To combat this the United States Navy began designing a 58,000 ton ship with an intended armament of twelve . This battleship took shape in the mid-1930s as USS Montana, the lead ship of her class of dreadnought battleships. She would have fielded three more guns than those mounted aboard the Iowa-class, a more powerful secondary battery of 5 in (127 mm)/54 caliber DP mounts, an increase in armor that was to enable Montana to withstand the effects of the caliber guns and the ammunition she and her Iowa-class sisters were to carry.
The increase in Montana’s firepower and armor came at the expense of her speed and her Panamax capabilities, but the latter issue was to be resolved through the construction of a third, much wider set of locks at the Panama Canal. As the situation in Europe deteriorated in the late-1930s, the USA began to be concerned once more about its ability to move warships between the oceans. The largest U.S. battleships were already so large as to have problems with the canal locks; and there were concerns about the locks being put out of action by enemy bombing. In 1939, to address these concerns, construction began on a new set of locks for the canal that could carry the larger warships which the U.S. had either under construction or planned for future construction. These locks which would have enabled Montana to transit between the Atlantic and Pacific Oceans without the need to sail around the tip of South America. As USS Montana, BB-65 would have been the only battleship class commissioned by the U.S. to have come close to equaling the Empire of Japan's s on the basis of armor, armament, and tonnage.
By 1942 the United States Navy shifted its building focus from battleships to aircraft carriers after the successes of carrier combat in both the Battle of Coral Sea, and to a greater extent, the Battle of Midway. As a result the construction of the U.S. fleet of s had been given the highest priority for completion in the U.S. shipyards by the U.S. Navy. The Essex-class carriers were proving vital to the war effort by enabling the Allies to gain and maintain air supremacy in the Pacific Theatre of World War II, and were rapidly becoming the principal striking arm of the United States Navy in the ongoing effort to defeat the Empire of Japan. Accordingly, the United States accepted shortcomings in the armor for their s, South Dakota-class battleships, and s in favor of their additional speed, which enabled these battleship classes to steam at a comparable speed with the Essex-class and provide the carriers with the maximum amount of anti-aircraft protection.
Like Kentucky, Illinois differed from her earlier sisters in that her design called for an all-welded construction, which would have saved weight and increased strength over a combination riveted/welded hull used on the four completed Iowa-class ships. Engineers considered retaining the original armor for added torpedo and naval mine protection because the newer scheme would have improved Illinois’ armor protection by as much as 20%. This was rejected due to time constraints and Illinois was built with an Iowa-class hull design. Funding for the battleship was provided in part by "King Neptune", a Hereford swine auctioned across the state of Illinois as a fund raiser, and ultimately helped raise $19 million in war bonds (equivalent to about $200 million in 2007 adjusted dollars).
Illinois’s keel was laid down at the Philadelphia Naval Shipyard, Philadelphia, Pennsylvania on 15 January 1945, but her construction was canceled after the atomic bombings of Hiroshima and Nagasaki. She was struck from the Naval Vessel Register on 12 August 1945. Her incomplete hulk (at the time 22% finished) was retained along with her sister USS Kentucky (BB-66) until 1958, when both ships were finally scrapped. She was broken up in her dry dock on the builder's ways starting in September 1958.
The ship's bell was cast and currently resides at Memorial Stadium at the University of Illinois at Urbana-Champaign; it reads USS Illinois 1946. While University of Illinois records are unclear as to whether the bell was donated to it or specifically to the Naval Reserve Officer Training Corps (NROTC) at the university, an Associated Press article published in 1983 seemed to indicate the latter. According to the AP, the bell had previously resided in a Washington museum until finding its new home with the Fighting Illini football team in 1982; since then, the bell is traditionally rung by NROTC members when the football team scores a touchdown or goal.