51-year-old software industry professional here near Chicago:
Jeans and shirt.
Will go for business casual for occasional internal meetings.
For customers, willing to match the customer, even if that means, gack, a suit and tie. (Although in 25+ years I can count those occasions on 1 hand and still have some fingers available for rude gestures.)
I detest dressing up for work and select jobs partially based on that. With my fashion sense, if I am judged by my wardrobe, I am already done.