As a native Marylander, I've had many discussions with friends about whether we can call it a Southern state. You could say it's in "Dixie," which (according to one historical interpretation from this Civil War fact book) means south of the Mason-Dixon Line. One could also argue that because it fought for the North in the Civil War, Maryland should be considered a Northern state. However, we can't forget that Maryland was a slave state that was chock full of Southern sympathizers during the war.
For evidence, just look up the official state song that remains on the books. You might be surprised (or perhaps offended) at the lyrics. According to this NPR story, a group of active fourth-graders were certainly offended when Linda Tuck, a school library "media specialist," led their study and discussion of the song. Here are some of the lines seen as offensive:
"The despot's heel is on thy shore, Maryland!"
"Huzza! She spurns the Northern scum!"
By the way, that "despot" refers to the revered Abraham Lincoln. James Ryder Randall wrote the poem in 1861, after riots in Baltimore led to the deaths of a few civilians, according to Dissonance by David Detzer.
Tuck took a vote and found that the school children wanted to see the lyrics changed. They then wrote letters to state delegates, and now a bill is in the works. Delegate Pamela Beidle, who introduced the bill, wants to use a different poem written in 1894 for the lyrics of the song.
According to a local news article, the bill does have its critics, who say that the song's a reminder of a part of Maryland's history that is too often forgotten. Others would simply rather leave it up to voters.