As recently as the 90's, Delta had mainline service between cities like Shreveport, Louisiana to Monroe, Louisiana or Jackson, Mississippi to Birmingham, Alabama. There were sometimes passengers.

The Shreveport service was a milk run, for example, DFW-SHV-MLU-ATL.

Express Jet flying as Continental Express flies from IAH-EWR stopping in one city in between, at least they did a few years ago.

A few years ago, one could fly from LaGuardia to Fayetteville, Arkansas on American Eagle and connect with a Fayetteville-Los Angeles flight. Transcon in a ERJ! I'm not sure if there's still an ERJ flight from Houston to Palm Springs but if there is there might be another ERJ from somewhere in the south to Houston. That would be a near transcon in an ERJ.