Chicago was always the center. Stern is the successor to Chicago Coin and Williams, having bought up the assets of those companies in bankruptcy.
Stern Electronics went under in the 80s and folks ended up at Data East, then Sega. Eventually Sega got out of pinball and sold the assets to Gary Stern, Sam's son, to form Stern Pinball. This was about the same time Williams got out of pinball, and I think their assets ended up at a German company.
Gary Stern started Data East Pinball with the remains of Chicago Coin (and then ripped off the electronic design from Williams). DE did indeed become Sega and then became Stern in 1994.
Williams shut their pinball division down in 1999 and the assets have been licensed out to various entities in the 20 years since. The remaining slot machine company (WMS Industries) was purchased by Scientific Games in 2013. SGI also owns...wait for it... the remains of Bally Gaming.