The Mill Inn had its beginning in the early 1890s when Capt. Scott K. Snively built a single elevator, steam powered, wooden milling structure at 245 Broadway, Sheridan, Wyoming (present location of RENEW). Capt. Snively sold the mill in 1895 to the Sheridan Milling & Mfg. Co., and in 1896 the mill produced 40 barrels of flour every 24 hours.

In 1903 the Sheridan Milling & Mfg. Co. was sold to J. W. Denio, a well-known miller from Longmont, Colorado. Because of the great demand for milled products, the Denio family enlarged and modernized the mill, operating it on a 24-hour basis until it was destroyed by fire in June, 1919. In 1920 a new mill representing the latest in milling technology, made of fire resistant steel reinforced masonry, was built by J. W. Denio Milling Co.; and it "opened in its new quarters in 1921" on the Big Horn paved road southeast of Sheridan (present location of the Mill Inn). By 1923 the J. W. Denio Milling Co. was the largest and most modern of its kind in Wyoming with daily capacity of 1,000 barrels of flour and pending plans of enlarging capacity. Quoting a Sheridan Post headline in 1932, "Largest Milling Plant in Wyoming Claims Sheridan as Home".

The milling facility encouraged the raising of wheat in the Sheridan valley and processed a heavy volume of grain from irrigated valleys in southern Montana. Until 1927 the mill was operated as the J. W. Denio Milling Co. with J. W. Denio president, Ralph Denio vice-president and manager, Fred Goldberger secretary/treasurer; and it stood as a monument to their faith in northern Wyoming and especially to the grain producing value of the areas soil. In 1927 the plant became known as the Sheridan Flouring Mills, Inc. when a group of interested, influential business people and ranchers bought the plant. New and better varieties of spring and winter wheats were introduced and local area farmers were encouraged to plant them. Advanced technology and the associated necessity of highly skilled millers required expanded markets for the finished products.

Because of the excellent quality of the product, bakers all over the United States readily accepted the flour. Additional demand for the finished product required building more structures for grain storage. Elevator storage increased from 150,000 bushels to 410,000 bushels by the addition of 10 concrete grain storage tanks at the plant site (still standing to the north of the Mill Inn). In addition, the Sheridan Flouring Mills Inc. owned 13 country elevators, located in Parkman, Ranchester, North of Sheridan, Wyarno, Buffalo, Arvada, Gillette, Clearmont, and Big Corrals; in Montana the elevators were located in Hardin, Garryowen, Lodge Grass and Wyola.

In 1934 the Sheridan Flouring Mills, Inc. was valued at $500,000, had 30-40 employees, paid $50,000-$60,000 to grain producers annually and was one of the largest taxpayers in Wyoming. Over 90% of the flour manufactured at the mill was sold outside of the local area to bakeries all over the U.S., thus bringing capital back to Sheridan where the bulk was spent and reinvested. Frequently upgraded as the industry changed, 100,000 to 125,000 barrels of flour were annually converted into "Best Out West" flour and Tomahawk Feeds" livestock and petfood. Sheridan Flouring Mills, Inc. annually converted 5,000 tons of Wyoming coal into steam and electric power for its operations and probably had the largest payroll and employee roster of any home-owned industry of its kind.

Prior to the purchase of the mill by Nebraska Consolidated Mill Company in 1963, Sheridan Flouring Mills, Inc. had total wheat storage capacity of 554,000 bushels at the mill site with the addition of the nine steel grain storage tanks. The mill required one million bushels of wheat annually, the major portion of which was grown in the Sheridan area. Approximately $2,000,000 was channeled into the local economy for wheat alone. Sheridan Flouring Mills, Inc. employed 75 people with an annual payroll of $350,000 paid over $100,000 per year in taxes, $750,000 in freight and $40,000 for electric power.

Due to changes in the entire structure of freight rates for grain and flour, ConAgra (formerly Nebraska Consolidated Mill Company) could no longer compete with other milling locations on flour shipped into areas of concentrated population. Milling operations were closed and the buildings, equipment and lands comprising the former Sheridan Flouring Mills, Inc. were sold in 1974. The actual mill building was remodeled into a 45-unit motel and the tower was converted into office spaces. The Mill Inn is listed on the National Register of Historic Places.