The opinion is here; here’s an excerpt from the concluding paragraph:
This court’s decision is based on the following and only on the following: (1) what it means to be a resident for election purposes was clearly established long ago, and Illinois law has been consistent on the matter since at least the 19th Century; (2) the novel standard adopted by the appellate court majority is without any foundation in Illinois law; (3) the Board’s factual findings were not against the manifest weight of the evidence; and (4) the Board’s decision was not clearly erroneous.
More on the now-reversed Appellate Court decision here. Two Justices concurred in the judgment, but opined that the law was not as clear as the majority said it was, and that it was therefore “unfair of the majority to state that the appellate court majority ‘toss[ed] out 150 years of settled residency law,’ adopted a ‘previously unheard-of test for residency,’ or was engaged in a ‘mysterious’ analysis.”
Thanks to commenter Morbo for the pointer.