The US Census says yes, Md is a southern state
https://www2.census.gov/geo/pdfs/maps-data/maps/reference/us_regdiv.pdf
Division 5: South Atlantic
Delaware (10)
District of Columbia (11) Florida (12)
Georgia (13)
Maryland (24)
North Carolina (37) South Carolina (45) Virginia (51)
West Virginia (54)
But Marylanders say no.
https://www.cbsnews.com/baltimore/news/maryland-considered-northern-state-goucher-college-poll/
BALTIMORE, Md. (WJZ) -- Is Maryland more northern or southern? The answer to that question depends on whom you ask, but most Marylanders say it's northern.
That's according to the results of a new Goucher College poll, which shows 65% of residents consider Maryland a northern state, more than double the 27% who view it as a southern state.
While the responses seem fairly cut-and-dried, the state's history is a little bit more complicated.
Maryland actually sits below the Mason-Dixon Line, which divided free states in the north from their slave-owning counterparts in the south during the Civil War era.
But ultimately, the consensus among residents from all walks of life -- regardless of age, gender, race, and political stance -- is that Maryland is a northern state.