Day was last seen at a Washrack in in the vicinity of the 100 block of St. Clair Avenue in National City, Illinois on August 10, 1990. She was getting into a semi truck at the time. She has never been heard from again.

One of Day's daughters had just had a baby prior to Day's disappearance. Day was very excited about the birth and introduced the baby to all her neighbors. This was the last time Day's daughters saw their mother. They reported her missing on August 12, but law enforcement did not begin to actually investigate Day's disappearance until 2004.

All of Day's possessions, including her toothbrush, were found missing from her home. Her boyfriend of seven years disappeared at the same time she did. Over a decade later, Day's daughter discovered he was incarcerated in a California prison for an unrelated crime. He has since been paroled. Day was unhappy with the relationship at the time of her disappearance and her loved ones feel the boyfriend may have been involved in her case. He maintains his innocence and has not been charged in connection with it, or even been questioned.

Day may have been involved with prostitution and/or drugs at the time of her 1990 disappearance. Her case remains unsolved.