1921

• The official State Seal of Wyoming in its present design is adopted by the Sixteenth Legislature and approved by the governor. lt becomes effective April 1.
• The State Historical Department, originally the State Historical Society, is organized.
• Teton County is carved from Lincoln County and Sublette County from Fremont and Lincoln Counties. To date, they are the last counties to be created in Wyoming.
• State Game and Fish Department is established. ^[1]

1922

• Teton County is organized.
• In strike situation, the Union Pacific stores a six months supply of coal along tracks.
• The Teapot Dome Oil reserve is secretly leased by the government to the Sinclair Oil Company for development.
• Standard Oil Company in Casper is said to have the largest processing plant in the world.
• Cheyenne has a free campground for tourists, offering electric lights, hot and cold water, toilet facilities, shower baths, laundry tubs, a community house, boating facilities, and a community store.

1923

• Sublette, the last of the present twenty-three counties in Wyoming, is organized.
• A tax of one cent per gallon is levied on all gasoline sold in Wyoming.
• June 23, Governor William B. Ross issues proclamation convening Seventeenth State Legislature in special session to consider Farm Loan Act and agreements relative to interstate streams. ^[2]
• Ninety-nine miners die in explosion at Kemmerer coalmine.
• State Department of Agriculture is established.
• The Memorial Hospital of Laramie County is dedicated to the memory of Frances Warren Pershing, daughter of Senator F.E. Warren, who died in a fire in California in 1915.

1924

• February 5, Joseph M. Carey dies at age seventy-nine, ending a long political career.
• Senator Warren obtains a three million dollar appropriation for federal aid to night flying.
• State receives $1,700,000 from oil royalties for schools.
• Governor William B. Ross dies in office, October 2. Frank Lucas serves as acting governor until an election can be held to name his successor. Ross's widow, Nellie Tayloe Ross, is approached by the Wyoming Democratic Party and asked to run for the office
• Nellie Tayloe Ross is elected governor November 5.
• State Highway Department begins experimenting with treating gravel roads with oil.

1925

• Nellie Tayloe Ross, elected to fill the two years of her husband's unexpired term, is inaugurated as governor of Wyoming, January 5. She is the first woman governor in the United States.
• Sinclair lease is upheld in the Teapot Dome case tried before Judge T. Blake Kennedy in Cheyenne.
• Wyoming produces three and one-half million pounds of honey.
• A gigantic landslide, the whole north end of Sheep Mountain, dams Gros Ventre River and forms Slide Lake,also known as Sudden Lake, and destroys the town of Kelley. The area becomes known as the Gros Ventre Slide.
• Colorado River Compact is ratified by the State Legislature. ^[3]
• "Layman" Game and Fish Commission is created, with six members appointed by the governor.

1926

• State Training School for Girls is established at Sheridan. It would later be called the Wyoming Girl's School.
• Queen Marie of Rumania visits the state.
• John E. Higgins, of Converse County, wills his estate of $500,000 to the State of Wyoming.
• The State Highway Department estimates that tourists spent between six and seven million dollars in the state during the summer.

1927

• February 5, the Nineteenth Legislature adopts the meadowlark as state bird.
• Wyoming Aeronautics Law is passed
• State Department of Commerce and Industry is created.
• May 18, flood waters washout part of Slide Lake and a wall of water destroys the town of Kelly and kills six people.
• Tuberculosis Sanitorium, later Sanitarium, is completed at Basin.
• Congress passes act enabling the Shoshones to sue in the Court of Claims for that portion of the reservation occupied by the Arapa­hoes since 1878.
• October 10, Following the Teapot Dome scandal, the U.S. Supreme Court rules that the oil property be returned to the government to which it legally belongs.

1928

• Cement plant is constructed in Laramie.

1929

• Senator Francis E. Warren dies at the age of eighty-five, after having served as U.S. Senator 1890-93 and 1895-1929.
• Old Age Pension Act becomes effective June 1.
• Each county is assigned a number to appear on its license plate.
• The state has eighty-seven miles of oiled roads.
• Governor Frank C. Emerson, in a proclamation dated December 5, calls special session of Twentieth Legislature.
• Patrick J. Sullivan is appointed to fill the unexpired term of Senator Warren.
• Grand Teton National Park is established.

1930

• Wyoming's population is 225,565.
• KDFN, first radio station in Wyoming,starts operation in Casper, February 19.
• Fort D.A. Russell is officially renamed Fort Francis E. Warren, honoring Senator Warren.
• The Shoshone Indians at the Wind River Reservation elect the first woman member of their tribal council. She is Mrs. Irene Kinnear Meade, granddaughter of Jim Baker.
• Wyoming license plates for motor vehicles are to be issued by the county treasurers, not through the office of Secretary of State as formerly. The County Treasurer transfers these funds to the State Department of Revenue.
• Six thousand people celebrate the 4th of July at Independence Rock. In the 1930s, Wyoming is plagued by both drought and depression.
• Wyoming has approximately 62,000 autos.