Restructuring my response from the linked thread above with some additions:
I would recommend Patricia Becker at Fireside Farm with every fiber of my being - the barn is gorgeous, she’s an exceptional trainer, her assistant is great when she’s showing/doing clinics, and it’s a short drive from the Northern Suburbs in Camp Lake, WI.
It looks like Sara Latokhin is operating out of Libertyville now - Independence Farms, shares space with Hunter/Jumpers.
Agree with Flying Dutchman Farm in Barrington - Julie Julian is still the head trainer but her daughter Rosie Julian-Simoes also takes on clients who are boarding and is a really wonderful teacher for both horse and rider.
Amanda Johnson is a really wonderful trainer and person. I believe she’s at Paris Farms now?
I can’t seem to find any info on the farm itself but Amy Walker-Basak trains out of Marquis Dressage and she’s got a great reputation.
Tempel Farms is always an option - they have a boarding program though I’m not positive who’s training out of there for their non-Lipizzaner horses.
Sunflower Farms has a great boarding program, but also not sure who the trainer on site is.
I’m not sure if KYB Dressage is taking boarders right now, but Kim and Yvonne also are great trainers with a long-standing reputation in the community.
If you’re willing to make the trek to Madison, Megan McIsaac at Lindinhof Equine Zestrum has a great contingent of boarding clients.
Heather McCarthy and Brittany Burson’s Paddock Hill Farms is also wonderful.
Wild Rose Farm - trainer is Katie Hiller - is absolutely beautiful. Katie is up and coming - still a U25, I believe, but studied under JJ Tate and has a great approach.
I’ve heard Cranewood Farm in St. Charles is getting a bigger dressage contingent and has Joan Pecora teaching lessons - she’s a tough but fair trainer. I think she’s also teaching at Double-W Stables in Gurnee?
It might be worthwhile heading to Lamplight for their first Dressage show May 20th-21st and ask around. It’ll also help you get a good idea of the talent here.
Good luck!