Missouri Abbreviation

Which Missouri abbreviation to use

The postal code never takes a period and is always written in capitals. The traditional form always takes a period. Mixing them, as in "M.O." or "Mo" without the period, is a common slip.

MO on envelopes, labels and web forms

Two letter state codes date to the 1960s, when the Postal Service set them up so that city, state and ZIP code would fit on one line for machine sorting. Missouri was assigned MO. Put it after the city, with no comma needed between the code and the ZIP code.

Online forms with a state drop down menu often list the codes in alphabetical order by state name, so MO comes after Mississippi and before Montana. Read slowly, because those neighbors start with the same letter.

Mo., the older short form, and news style

Long before those codes existed, Mo. was the usual short form for Missouri. You will still see it in older books, legal citations and some formal style guides.

News writing follows its own rules. Under the common newsroom style, state names are spelled out in the body of a story. Mo. is used in datelines at the start of an article, in photo captions and in places where space is short, such as a list of election results. A few very large cities, St. Louis among them, are well known enough that newsroom style lets them stand alone in a dateline.

The Missouri state abbreviation and its look alikes

Eight state names begin with M, so Missouri's code is easy to confuse with a neighbor on a list.

• MO is Missouri.
• MS is Mississippi.
• MN is Minnesota.
• MT is Montana.
• MI is Michigan.
• MD is Maryland.
• ME is Maine and MA is Massachusetts.

A helpful habit: MO is simply the opening pair of letters in Missouri. That shortcut does not work for every state (Mississippi is MS, not MI), so check the full list on the state abbreviations page when in doubt.

MO outside of addresses

The same two letters have other jobs. In crime stories and casual speech, MO can mean modus operandi, a person's usual way of doing something. In some workplaces it means mail order or money order. Context makes it clear: when it follows a city name and comes before a ZIP code, it means the state. The MO stands for page covers those other meanings.

Writing tips for Missouri

• Spell out Missouri when it stands alone in a sentence: "Missouri borders eight states."
• Use MO in a full mailing address, every time.
• Use Mo. only when your teacher, editor or style guide asks for traditional forms.
• Never use MO for the state in the middle of a formal sentence.
• Put a comma after the state in running text: "She lived in Hannibal, Missouri, for ten years."