The first residents of Cornwall consisted of a hand-full of white settlers, of English stock, seeking land on which to build a home and raise crops and livestock. They came primarily from elsewhere in Connecticut and Massachusetts. In 1738, lots consisting of about 50 acres, each, were auctioned off by the Connecticut legislature, and by 1740 when Cornwall was incorporated, about 40 men with their families were settled in this remote town.

The early settlers were faced with the daunting task of clearing the thick forest and removing the multitude of large rocks that littered the landscape and created a hazard for plowing and tilling. This was mainly accomplished by manual labor with only a few oxen to help pull large boulders and felled trees. They soon found that hills and rocky soil made for a beautiful countryside, but poor farming. They overcame incredible hardships including severe winters and disease, but in time their dedication and perseverance paid off with sufficient crops and livestock to sustain the settlers. By 1760 Cornwall was established with church, school, town meeting site, and roads connecting them to Kent and Litchfield and a population of between 500 to 600 residents.

Between 1760 and 1825 Cornwall continued to grow. Bad roads and lack of nearby markets made anything other than subsistence farming difficult but not impossible. Enterprising men like Major John Sedgwick and Capt. Edward Rogers could not make poor soil fertile or hilly land flat, but they could build iron forges, potasheries, and sawmills, and even by buying up enough land, engage in commercial agriculture on a moderate scale. By 1820 the population had reached 1,662 residents and farming had become sufficiently productive to yield crops of wheat, rye, corn, flax, wool, tobacco, dairy products and beef. Production in excess of their basic needs provided them with surplus crops to sell or trade, providing a measure of prosperity for the town.

Despite their physical isolation the residents of Cornwall took an active part in the Revolution and politics. A number of Cornwall men distinguished themselves in the Revolutionary War including General Sedgwick, Ethan Allen, Judge Oliver Burnham, Gen. Heman Swift, and Capt. Edward Rogers. Cornwall's patriotism was not limited to the battlefield, as some of its more prominent citizens were elected to represent the town at the State level. Some of those elected to multiple terms included Benjamin Gold, Major Sedgwick, Judge Oliver Burnham and Noah Rogers.

In 1780 Cornwall experienced a religious crisis. The parishioners of the Congregational Church refused to pay the pastor of 20 years, Rev. Hezekiah Gold, his salary and locked him out of his church. The reason for all this seemed to be both financial and personal. There was a resulting schism in the congregation which lasted for years and led to the building of a second Congregational Church, attended by the "Strict Congregationalists", while those loyal to Rev. Gold remained with the first church. Both churches have survived, however, the Second Congregational Church, originally located at the town center, was rebuilt in North Cornwall around 1826 on land donated by Noah Rogers.

Also of historical religious significance was the establishment of a Foreign Mission School in Cornwall, which lasted from 1817 to 1826. The American Board of Foreign Missions decided to establish a school in Cornwall to train the natives of non-European races to become missionaries to their own peoples. They chose Cornwall because of its remoteness from the city allurements and the persuasion of the Cornwall pastor, Timothy Stone. The school, attended by a number of American Indians and Hawaiian natives, attained celebrity status and brought national attention on Cornwall.

The period between 1820 and 1900 for Cornwall coincided with the industrial revolution, which began with expansion and then decline toward the end of the century. Industrialization led to specialization in farming, resulting in fewer but larger farms. Toward the end of the century the production of milk, butter and cheese on Cornwall farms had replaced the crops of the past century. While small industries flourished there early in the century, they vanished toward the end, because they could not compete with larger industries located elsewhere. Due to emigration, the population decreased to below 1000 residents toward the end of the 19th century from a high of 1,953 in 1860.

In the Civil War, Cornwall was the main contributor of soldiers for the Lichfield County Regiment, furnishing some 250 men. At Cold Harbor this regiment suffered more casualties than any other regiment on either side in any single battle of the whole war. Killed in this battle was Capt. Amos T. Allen. Another famous member of the Sedgwick family, Maj. Gen. John Sedgwick, was killed in 1864 at Spottsylvania. Other tragic losses included John Oliver Hart and Noah Miner Pratt, killed in 1862 at Wilmington Island, Georgia.

The trend toward fewer farms and younger residents leaving to find opportunities in the larger cities has continued to the present day. The old school house has been converted to library open only several days a week. There are few commercial establishments consisting only of a small furniture factory, several country stores, and only a few establishments catering to tourists. There are no restaurants or motels. There is not a clearly defined town center nor are there any historical markers. Only a hand-full of descendants from the old prominent families remain, and as they leave their land is being bought by out-of-towners. The countryside retains its original beauty, but only a few remember those early colonists who labored and fought and contributed to the history of our Republic.