According to Dan Kassebaum's website, this is the fifth state record. Remarkably, it is the fourth for Cook County.
I actually saw the one that wintered in Lincoln Park. I had just started my first internship at the Field Museum as a high school freshman and talked my mom into stopping at the Bird Sanctuary to look for the Brewer's Sparrow on our way down to the museum.
May 26, 1982, Jackson Park, Cook County (Paul Clyne)
May 29, 1986, Cook County (specimen - FMNH) (Dave Willard)
November 27, 1996 - May 1997, Lincoln Park, Cook County (Bob Hughes)
December 4, 1998, Midewin National Tallgrass Prairie, Will County (Doug Stotz)