In or around 1905, Samuel P. Colt purchased and consolidated the Chase, Church and Van Wickle farms. He built a summer house ("The Casino") on the grounds, as well as a stone barn to accommodate a prize herd of Jersey cattle. The marble gates of the main entrance, modeled after the approach to the Petit Trianon at Versailles and unveiled in 1913, bear an inscription: "Colt Farm, Private Property, Public Welcome".
Colt died in 1921, and the lands passed to his Industrial Trust Company. According to the previsions of Colt's will, the farm remained open to the public. Over time, the grounds suffered from vandalism, and a number of statues were destroyed, stolen, or relocated for safe keeping.
In 1965, the State of Rhode Island purchased Colt Farm, and on August 21, 1968, the lands were dedicated as Colt State Park by Rhode Island Governor John Chafee. A statue of Chafee now stands in the park.