Maryland was first recognized as a "Free State" on November 1, 1864. On that date, the Maryland Constitution of 1864 took effect. By its provisions, slavery within the State's borders was abolished, and Maryland, indeed, became a free state. To celebrate the emancipation, under direction of the Baltimore City Council, five hundred guns were fired, bells were rung, and flags displayed "to attest the joy of the people at their great deliverance."
Much later, the nickname "Free State" was used in a different context by Hamilton Owens, editor of the Baltimore Sun. In 1923, Georgia Congressman William D. Upshaw, a firm supporter of Prohibition, denounced Maryland as a traitor to the Union for refusing to pass a State enforcement act. Mr. Owens thereupon wrote a mock-serious editorial entitled "The Maryland Free State," arguing that Maryland should secede from the Union rather than prohibit the sale of liquor. The irony in the editorial was subtle, and Mr. Owens decided not to print it. He popularized the nickname, however, in later editorials.
FuzzyDave does it again -- FTF glory is his