Sent in May, 1630, by the Virginia council to watch the movements of Lord Baltimore, he co-operated in England with ex-Governor Francis West, of Virginia, Sir John Wolstenholme, and other gentlemen who wished the restoration of the London Company.
Aided by these friends, Claiborne defeated the proposed grant, but Baltimore persevered, and, in April, 1632, received from the crown a patent for a portion of the Virginia territory lying north of Point Comfort, and having for bounds the ocean, the fortieth parallel of north latitude, the meridian of the western fountain of the Potomac, the southern bank of the Potomac River, and a line drawn east from Watkins Point.

In the grant the land was described as "hitherto unsettled and occupied only by barbarians ignorant of God." The king first proposed to call it Mariana, in honor of his wife, Henrietta Maria, but on Baltimore objecting that it was the name of a Spanish historian who had written against the doctrine of passive obedience, Charles modified the appellation, and said, "Let it be called Terra Mariae--Maryland."[7] April 15, 1632, George Calvert died, and the charter was made out in the name of his eldest son, Cecilius, and was signed by the king, June 20, 1632.

Cecilius Calvert, named after Sir Robert Cecil, was born in 1605, and in 1621 entered Trinity College, Oxford University.

He married Anne Arundel, daughter of Lord Thomas Arundel, of Wardour.

As Cecilius, unlike his father, never held public positions in England, his character is best revealed by his conduct of his province in America, which shows him to have been a man of consummate prudence and tact.
Baltimore's grant called forth a strong remonstrance from members of the Virginia Company and all the leading planters in Virginia, including Claiborne.