1903 in the United States

Federal government

• President: Theodore Roosevelt (R-New York)
• Vice President: vacant
• Chief Justice: Melville Fuller (Illinois)
• Speaker of the House of Representatives:

David B. Henderson (R-Iowa) (until March 4)

Joseph Gurney Cannon (R-Illinois) (starting November 9)

• Congress: 57th (until March 4), 58th (starting March 4)

January–March

• January 4 – Topsy, a female Asian circus elephant, is killed by electrocution at Luna Park, Coney Island, New York City.
• January 17 – 13 days after Topsy's death, the Edison Manufacturing Company released the short, black-and-white, silent documentary film Electrocuting an Elephant, showing the footage of Topsy's electrocution.
• January 19 – The first west-east transatlantic radio broadcast is made from the United States to England (the first east-west broadcast having been made in December 1901).
• January 21 – Section of Militia Affairs within the Adjutant General's office.
• February 11 – The Oxnard Strike of 1903 becomes the first time in U.S. history that a labor union is formed from members of different races.
• February 14
  • Census Board within the Department of Commerce and Labor (Census Bureau).
  • Department of Commerce and Labor founded
  • United States Coast and Geodetic Survey transferred to the Department of Commerce and Labor.
• February 15 – Morris and Rose Mitchom introduce the first teddy bear in America.
• February 23 – Cuba leases Guantanamo Bay to the United States "in perpetuity".
• March 2 – In New York City, the Martha Washington Hotel, the first hotel exclusively for women, opens.
• March 14 – The Hay–Herrán Treaty, granting the United States the right to build the Panama Canal, is ratified by the United States Senate. The Colombian Senate later rejects the treaty.

April–June

• May 16 – 8:05pm: Luna Park, Coney Island, New York, opens.
• June 12 – The Sigma Alpha Iota International Music Fraternity is founded at the University of Michigan School of Music.
• June 14 – Heppner Flood of 1903: The town of Heppner, Oregon, is nearly destroyed by a cloudburst that results in a flash flood.

July–September

• July 1 – U.S. Bureau of Fisheries within the Department of Commerce and Labor.
• July 6–10 – Evansville race riot in Evansville, Indiana.
• July 7 – "Mother" Mary Harris Jones starts a "Children's Crusade" ("March of the Mill Children") from Kensington, Philadelphia to Oyster Bay, New York, the hometown of President Roosevelt, with banners demanding "We want to go to school and not the mines!"^[1]
• July 23 – Dr. Ernst Pfenning of Chicago becomes the first owner of a Ford Model A.
• August 9 – Commanding General post replaced by that of Chief of Staff of the Army.
• September–October – A mysterious "visitor" is reported in Van Meter, Iowa.
• September 3 – Los Angeles real estate investor Griffith J. Griffith shoots his wife in the face at the Arcadia Hotel in Santa Monica.
• September 11 – The first stock car event is held at the Milwaukee Mile.
• September 15 – Miami Herald first published as The Miami Evening Record.
• September 27 – The Wreck of the Old 97 engine at Stillhouse Trestle near Danville, Virginia, which kills nine people, inspiring a ballad and song.

October–December

• October – Frank Nelson Cole proves that 2⁶⁷-1 is composite by factoring it as 193,707,721 * 761,838,257,287 after trying for every Sunday over three years.
• October 1 – The first modern World Series pits the National League's Pittsburgh against Boston of the American League.
• November 2
  • Maggie L. Walker becomes the first African American woman to charter a bank.
  • Lyceum Theatre (Broadway) opens, making it the oldest continuously operating legitimate theater in New York City.
• November 4 – With the encouragement of the United States, Panama proclaims itself independent from Colombia.
• November 13 – The United States recognizes the independence of Panama.
• November 18 – The Hay–Bunau-Varilla Treaty is signed by the United States and Panama, giving the U.S. exclusive rights over the Panama Canal Zone.
• November 23 – Colorado Governor James Hamilton Peabody sends the state militia into the town of Cripple Creek to break up a miners' strike.
• December 17 – Orville Wright flies an aircraft with a petrol engine at Kitty Hawk, North Carolina, in the first documented, successful, controlled, powered, heavier-than-air flight.
• December 19 – Williamsburg Bridge opens.
• December 30 – A fire at the Iroquois Theater in Chicago kills 600.

Undated

• The Lincoln–Lee Legion is established to promote the temperance movement and signing of alcohol abstinence pledges by children.
• The first box of Crayola crayons is made and sold for 5 cents. It contains 8 colors; brown, red, orange, yellow, green, blue, violet and black.
• Coca-Cola removes cocaine as a key ingredient from their formula; up to this time, it has contained approximately nine milligrams of cocaine per glass.

Ongoing

• Progressive Era (1890s–1920s)
• Lochner era (c. 1897–c. 1937)