In 1659, when a group of English investors purchased shares in Nantucket, they set off homestead lots for each shareholder, and the rest of the island was held in common for livestock grazing. This was the Common and Undivided Land.
By 1714, sale, purchase, and inheritance of the original twenty-seven shares had led to many individuals holding complex fractions of shares. Seeking to assign a value to these fractions, the Proprietors decided to divide each of the twenty-seven shares into 720 units to be known as “sheep commons.” For each 1/720th of a share, an owner was permitted to graze one sheep on the Common and Undivided Land. By a variable formula, a certain number of sheep was equivalent to a smaller number of horses or cows. For instance, at one time, if one owned eight sheep commons, one had the right to graze eight sheep, or one might instead graze one horse or two cows.
By 1821 the Massachusetts Supreme Court had ruled that anyone who held at least 100 sheep commons had the right to exchange his grazing rights for a set-off piece of land as private property. Following this decision, several holders of large numbers of sheep commons converted portions of the Common and Undivided Land to private ownership. This radically reduced the area of the remaining Common and Undivided Land. Most of those who still retained sheep commons were smallholders.
By 1882 there were just one hundred proprietors holding 1300 sheep commons, and these individuals only held on average between one and ten sheep commons. In 1903 the number of proprietors was down to seventy-seven. In 1956 the Town of Nantucket purchased 565 sheep commons and by 1988, through additional acquisition came to hold 610, giving the Town of Nantucket controlling interest in the last vestiges of the Common and Undivided Land.