Off the top of my head Koopman Lumber in Grafton and Morse Lumber in Southbridge. I'm not a woodworker so I don't really know how they stack up against other options but my Father and Grandfather both were and that's who they used.

When I was a carpenter, we went to crossroads sawmill because it was pretty close, theres a few around. I heard winwood sawmill in Winchendon is better for craftzmen specifically. They have a kiln and some other workshop tools that most people dont have.

I only needed special wood for special projects.

Another place to ask for a reference is the Worcester Center For Crafts on Sagamore street in Worcester. Lots of high end artisans there to give you some leads.

Thank you all for your responses! I have a few good leads now and I really appreciate it—I’m looking forward to making some sawdust!

Aside from finding a guy who has a band mill and works out of his garage, there's really nothing particularly close by. Rugby/Downes & Reader in Stoughton, Highland in Brentwood NH, Forest Products in Greenfield, Rex or McIlvain in CT if youre buying quantity. For smaller quantity and really good (and pricey) quality I'd go to Forest.

edit: all these places sell in the rough - your options for dimensioned might be somewhat limited (I always bought rough, so not entirely sure).

Pirner Lumber in Hubbardston

Plenty of solid recommendations in here, but nobody has mentioned the best answer -- Barrette's Hardwood, which is just over the border in Thompson, CT. They specialize in domestic hardwoods. You'll have a range of widths and thicknesses to choose from, and pretty much everything is dimensioned. They also have a staggering selection of live edge wood as well if you're interested in that. Their prices are higher than the other suppliers I use for my business (Goosebay Lumber and Highland Hardwoods, both in NH), but they have by far the best overall selection in the Worcester area.

facebook marketplace has tons of people selling. lots of questionable stuff (green) and so many trying to capitalize on trend (OMG LIVE EDGE SLAB FARMHOUSE) but if you can sift through the chaff you'll find there are plenty of guys running small mills who even have kilns and they're almost always willing deal.

FIL is big into woodworking, he tends to head to Rockler in Cambridge.