In 1629 George Calvert, 1st Baron Baltimore, applied to Charles I for a new royal charter for what was to become the Province of Maryland, which was at the time the northern part of Virginia. George Calvert died in April 1632, but a charter for "Maryland Colony" (in Latin, "Terra Maria") was granted to his son, Cęcilius Calvert, 2nd Baron Baltimore, on June 20, 1632. The new colony was named in honor of Henrietta Maria, Queen Consort of Charles I .
On March 25, 1634, Lord Baltimore sent the first settlers into this area, which would soon become one of the few predominantly Catholic regions among the English colonies. Maryland was also one of the key destinations of tens of thousands of British convicts. The Maryland Toleration Act of 1649 was one of the first laws that explicitly dictated religious tolerance (as long as it was Christian). The act is sometimes seen as a precursor to the First Amendment.
Based on an incorrect map, the royal charter granted Maryland the Potomac River and territory northward to the fortieth parallel. This proved a problem, because the northern boundary would put Philadelphia, the major city in Pennsylvania, within Maryland. The Calvert family, which controlled Maryland, and the Penn family, which controlled Pennsylvania, engaged two surveyors, Charles Mason and Jeremiah Dixon, to survey what became known as the Mason-Dixon line, which would form the boundary between their two colonies and would later become the dividing line between North and South.