I'm retired and live in MA. I worked a temp job at my old company in CT but I was hired through the local office of a recruiter based in MD. Where do I file state taxes?

Yes, you are correct.  Since you live in MA you file a resident return there with all income.  Since you worked in CT and never lived there, you file non-resident there and only allocate the wages earned in CT.  You should work the non-resident state first (after federal entries) and take note of the income taxed and income tax applied by CT.  Those numbers will be used to claim a credit on your MA resident return for taxes paid to another state.  TurboTax should transfer the figures to your resident return and you should verify/edit as needed.

MD is simply the address of the employer administrative office and has no bearing on your taxes.