What is now known as Grant County was under the flags of Spain, England and France until it came under the flag of the United States in 1803 with the Louisiana Purchase from France. It became a part of Dakota Territory in 1861 when President James Buchanan signed the bill as one of his last official acts the first few days of March 1861.

From 1803 to 1861 it had been part of the territories of Indiana, Michigan, Wisconsin, Iowa and Minnesota. From 1861 to 1873 this area was part of Red River County from the Canadian border to Sioux Falls, along the Minnesota line. It was 450 miles long. In 1873 the county was named after president U.S. Grant and size much reduced, but covering much of present Deuel, Codington, and Roberts Counties as well as the present area. It was organized in 1878 at Inkpa City. It was not until 1883 that it became permanently organized. In 1892 the Sisseton Indian Reservation was open to settlers, adding Blooming Valley, Farmington and Lura townships in the extreme west end to Grant County.

Grant County was named for President Ulysses S. Grant because there were many Civil War veterans in the area. The county was designated by the legislature in 1873 and was first organized at a meeting on June 12, 1878, the county seat was located at Inkpa City (now Big Stone City). The first election was held in November, 1878. The organization of the townships was approved on July 25, 1881. After a vicious political struggle, the county seat was moved to Milbank in 1881.

The Hastings and Dakota Division of the Chicago, Milwaukee and St. Paul Railroad moved through Grant County in July, 1880, and facilitated the growth of the county. By 1925 the population had grown to 11,114; in 1980 the population was 9,013. Grant County is populated for the most part by people from New England, the Middle Atlantic States and the Midwest and immigrants from Sweden, Norway, Germany, Ireland and Canada.

The principle communities include Milbank, Big Stone City, Twin Brooks, Revillo, LaBolt, Strandburg, Stockholm, Marvin and Troy. Special points of interest include Blue Cloud Abbey near Marvin; Big Stone Cheese Factory and the coal burning Big Stone Power Plant; Valley Queen Cheese Factory, the historic grist mill and the granite quarries near Milbank; Big Tom, an especially large, isolated glacial hill; an old Indian church (founded in 1878) at Stockholm; and the view from the crest of the hills near Summit and Stockholm.

Grant County is immediately south of the fifth standard parallel. It has an area of 426,240 acres or 691 square miles. The Minnesota River Valley occupies the east end extending west to a line running from southwest of Revillo to Osceola Township. The valley is quite level, sloping gently toward the east and cut by numerous creeks and watercourses flowing from the Coteau westward. Within this valley, Whetstone Creek and its larger branches have cut narrow valleys of considerable depth, and the land east of Milbank bordering on this stream, as well as that near Big Stone Lake, is quite rolling. A stone moraine, of no great height and sometimes indistinctly developed, runs from the northwest corner of Big Stone Township east of Lake Albert to the southeast corner of Alban Township.

The altitude ranges from a low point of 962 feet (the lowest spot in South Dakota) on Big Stone Lake to 1,600 feet in the hills to 2,000 feet at the crest of the Coteau.

Sources: Centennial Atlas of Grant County South Dakota 1989 Atlas of Grant County South Dakota 1966