I'm looking for this novel (or maybe a series of books?). I remember that technology began failing all over the world. Some people began transforming into different types of mythical creatures, like sprites, demons, etc. There was a band of about four travelers that were trying to make it to Chicago, since that seemed to be at the center of the issue. The story line frequently shifted the point of view in each new chapter. I vaguely recall a final battle in Chicago with an enormous and powerful demon creature. I think this demon used to be a corporate lawyer or big business guy before his transformation. I believe I read this in the early/mid 2000s, and was likely published around that time because of the types of tech used and failing in the story. Although it bears some surface similarity to the TV show, Revolution, they aren’t comparable in plot or characters.
It’s the Magic Time series by Marc Zicree, summary of the first book:
For rising young lawyer Cal Griffin, it's just another day in the Big City -- until the lights go off ... for good. Suddenly packs of pale crouched figures are stalking the darkened subways, monsters prowl Times Square, and the people all around Cal are ... changing. Similar weirdness is happening everywhere, from the dank, cold heart of a West Virginia coal mine to a remote lab in South Dakota -- where a team of government scientists has unwittingly invited something catastrophic into the world -- to the highest levels of power in Washington, D.C. And Cal Griffin is not the only one struggling to comprehend the surreal, devouring chaos surrounding him -- nor the only one who will be forced to accept a new role in this brave new world of nightmare and wonder. For the forces bled from the stilled machines are fueling a consciousness both newly born and ancient -- and more than one unlikely hero will be needed for the titanic battle between the darkness and the light.
It looks like Chicago is more of a factor in the later books in the series, such as Angelfire:
In Zicree (The Twilight Zone Companion) and Bohnhoff's (The Spirit Gate) engrossing sequel to last year's Magic Time, Cal, Colleen, Goldie and Doc continue their quest for Cal's sister, Tina, a captive of the magical Source centered in Chicago. They journey from New York through a contemporary America where magic has wreaked havoc and come across the Preserve, where they recruit half-Lakota musician Enid Blindman, who can defend humans against the creations of the Source. In Chicago the company has to try freeing Enid from the Primal, the local supernatural presence, who turns out to be a golem under control of another formerly human minion of the Source. And so the quest goes on—which most readers will consider good news, as this is an intelligent variation on the quest theme as exemplified by Stephen King's The Stand. The story doesn't repeat itself; the characters grow (witness the relationship emerging between the ferocious army-brat survivalist Colleen and nurturing Chernobyl survivor Doc Lysenko); and the ultimate secret of the Source is sufficiently well hidden that several more volumes seem logically justified. The book doesn't escape the current saga-mongers' problem of losing some emotional impact for new readers, but the series will probably win a strong SF/fantasy following as long as future installments keep up the high quality.
The main events of the Word and Void series take place in Hopewell, Illinois, where a demon is attempting to subvert Nest Freemark, and is thwarted by Knights of the Word (Precursors to the druids). Part of this was pursuit of a Gypsy Morph, or embodiment of wild magic that always signifies a significant change.
The first book of the next group details the nuclear armageddon, and the rise of mutated creatures, and a trek back to Hopewell to visit Nest's grave, and get a hand that acts as a compass. This leads the Knight, Logan Tom, to Seattle. It is here we are also introduced to the Ellcry's and the Elves for the first time, as their magic is failing and demons are leaking in from the Forbidding. This leads to a migration, and subsequently into the whole Shannara series.
The Word and the Void was published from 1997 - 1999, with Armageddon following in 2006.