Calvert County was founded on July 3, 1654. Only three counties in the state are older: St. Mary's founded in 1637, Kent in 1637 and Anne Arundel in 1650. The first colonist came to the county soon after the arrival of the Ark and Dove in 1634.

Captain John Smith explored the Chesapeake Bay Country and, sailing past the Cliffs  of Calvert, wrote as follows: "The Western Shore, by which we sailed, we found well watered, but very mountainous and barren, the valleys very fertile, but extremely thick of small woods, as well as trees, and much frequent with wolves, bears, deer, and other wild beasts. The streams were crystal clear, and full of fish.

The first settlements in Calvert County, at the lower Patuxent and on St. Leonard's Creek, were probably made soon after the colonists arrived in St. Mary's. The earliest records appear in the minutes of the General Assembly in 1642. The growth of the county during the next fifty years was rapid. During this half century the county was settled by colonists, many of whom were highly educated for their time.

As originally established Calvert County comprised what is now Charles, Prince George's and parts of Montgomery and Frederick counties. In 1696 when Prince George's County was established, Calvert was reduced almost to its present proportions.

The early history of Maryland and of Calvert County was closely tied to political affairs in England. The county was established by Lord Baltimore. When the Puritans under Oliver Cromwell crushed the armies of Charles I in England, Lord Baltimore thought it wise to cultivate the friendship of the Puritans and sent his friend, Robert Brooke, a Protestant, to organize and govern the county. He arrived with his wife, ten children and 28 servants in June 1650. He was followed by many families representing the gentry of England.

When the Puritans were driven out of Virginia many of them settled in Maryland. Some of them, under the leadership of Richard Preston, settled in Calvert County. The two plantation houses built by him about 1650 on the lower Patuxent are still standing. One of them, known as Charlesgift, was the site of the first assembly held in Maryland. Here in 1655, an armed band of Gov. Stone's men from St. Mary's took the Puritans by surprise and seized the papers and documents that had been taken from St. Mary's by the Puritans.

The great seal of Maryland was lost in this raid and it has never been recovered. It is believed buried in the garden or hidden in the walls of the old house. The former owners of Charlesgift, Capt. and Mrs. Don Smith, state that they never hit a piece of metal when digging around the place without a feeling of anticipation. Perhaps one day the seal will be found.

Not only the Puritans, but many Quakers and Scotsmen came to Calvert County and many of the names of these early settlers are woven into its history. The time between the Revolutionary War and the Second War with England in 1812 was a time of uneventful growth in Calvert County. The plantation system developed and much of the cultural, as well as the social and political, life of the county was tied to this.

One of the most famous naval engagements in Maryland history took place in the Patuxent River in 1814. Of the few large naval vessels in the American Navy, none could be spared for the defense of the Chesapeake. This was left to Commodore Joshua Barney and the small flotilla of barges under his command. These barges were propelled by oarsmen and it was thought they would have an advantage over the wind-driven British ships. However, the newly developed European rockets had a greater range than the cannons of the American barges. The barges were forced to find haven in St. Leonard's Creek which was too small for the British vessels.

The British blockaded the entrance to the creek and a five-day battle ensued. Finally, the British withdrew because of damage inflicted by American vessels. During this time the British put ashore many raiding parties that pillaged, burned and destroyed much property. Many of the old plantation homes were burned or badly damaged.

After the War Between the States, Calvert County faced a difficult period of adjustment. The plantations were without an adequate labor force. Many of the old plantations were abandoned and the owners looked to Washington or Baltimore for employment.

Calvert County has contributed many illustrious names to the pages of history. Thomas Parran was Surgeon General of the Armies during the Revolutionary War. Two "first ladies" had their homes here. Louisa Catherine Johnson became the wife of President John Quincy Adams and Margaret Mackall Smith married President Zachary Taylor. Perhaps the best known was Roger Brooke Taney, whom President Andrew Jackson appointed Attorney General of the United States, Secretary of the Treasury, and finally Chief Justice of the Supreme Court. He held this position from 1836 to 1864 and wrote many opinions that have been important in legal history. One of the most famous was his decision in the Dred Scott Case.

Calvert County probably has as many historical old homes and churches within her borders as any place of comparable size in the United States. Christ Church, in the southern part of the county, Saints Church, in the upper county, was established as a parish in 1692. The present church was erected in 1774. Many beautiful and historic houses date back to the Colonial Period and can be visited at the same time of the House and Garden Tour in the county.