Federal government

• Articles of Confederation (through March 3):
  • 10th Confederation Congress
• United States Constitution (beginning from March 4):
  • President: George Washington (no political party-Virginia)
  • Vice President: John Adams (no political party-Massachusetts)
  • Chief Justice: John Jay (New York) (starting October 19)
  • Speaker of the House of Representatives: Frederick Muhlenberg (starting April 1)
  • Congress: 1st United States Congress (starting March 4)

January–March

• January 7 – The 1789 United States presidential elections and House of Representatives elections are held.
• January 21 – William Hill Brown's anonymous sentimental epistolary novel The Power of Sympathy: or, The Triumph of Nature, usually considered the first American novel, is published in Boston.^[1]
• January 23 – Georgetown University is founded in what would become Washington, D.C., becoming the first Catholic college in the United States.
• February 4 – George Washington is unanimously elected the first president of the United States by the United States Electoral College.
• March 4 – At Federal Hall in New York City, the 1st United States Congress meets and declares the new United States Constitution to be in effect.
• March 29 – Thomas Collins, President of Delaware, dies in office.

April–June

• April 1 – At Federal Hall, the United States House of Representatives attains its first quorum and elects Frederick Muhlenberg of Pennsylvania as its first Speaker of the House.
• April 6 – At Federal Hall, the United States Senate attains its first quorum and elects Senator John Langdon as its first president pro tempore; the first joint session of Congress is held on that same date, and the electoral votes of the first presidential election are formally counted. General George Washington is declared President-elect, and John Adams is declared Vice President-elect.
• April 21

• John Adams takes office as Vice-President of the United States and begins to preside the sessions of the United States Senate.
• George Washington's reception at Trenton is hosted by the Ladies of Trenton as he journeys to New York City for his first inauguration.

• April 30 – George Washington is sworn in at Federal Hall in New York City, beginning his term as the first president of the United States.

July–September

• July – Charles Thomson resigned as secretary of Congress and hands over the Great Seal, bringing an end to the Articles of Confederation.
• July 4 – Congress passes its first tax on 30 different items at 8.5% with discount to American ships over foreign ones.^[2]
• July 27 – The first U.S. federal government agency under the new Constitution, the Department of Foreign Affairs (later renamed the Department of State), is established following the month-long Decision of 1789, the first significant construction on the meaning of the U.S. Constitution in Congress.
• August 7 – The United States Department of War is established.
• September 2 – The United States Department of the Treasury is established.
• September 15 – The Department of Foreign Affairs is officially renamed the Department of State.
• September 24 – The Judiciary Act of 1789 establishes the federal judiciary and the United States Marshals Service.^[3]
• September 25 – The United States Congress proposes a set of 12 amendments for ratification by the states. Ratification for 10 of these proposals is completed on December 15, 1791, creating the United States Bill of Rights.
• September 29 – The U.S. Department of War establishes the nation's first regular army, with a strength of several hundred men.

October–December

• November 6 – Pope Pius VI appoints John Carroll the first Roman Catholic bishop in the United States.
• November 20 – New Jersey ratifies the United States Bill of Rights, the first state to do so.
• November 21 – North Carolina ratifies the United States Constitution and becomes the 12th U.S. state (see History of North Carolina).
• November 26 – A national Thanksgiving Day is observed in the United States as recommended by President George Washington and approved by Congress.
• December 11 – The University of North Carolina, the oldest public university in the United States, is founded.

Undated

• Thomas Jefferson returns from Europe, bringing the first macaroni machine to the United States.
• Influenced by Dr. Benjamin Rush's argument against the excessive use of alcohol, about 200 farmers in a Connecticut community form a temperance association.
• Rev. Elijah Craig begins commercial distillation of Bourbon whiskey in Fayette County (approximate date).
• Fort Washington is built in Cincinnati, to protect early U.S. settlements in the Northwest Territory.

Ongoing

• Northwest Indian War (1785–1795)