When you're writing an envelope or filling out an online shipping form, you often run into the two-letter code MD. In geographic and postal contexts, MD stands for Maryland, one of the original thirteen colonies and a vital Mid-Atlantic state. While multiple states start with the letter M, MD was assigned as the unique standardized identifier for Maryland to streamline mail delivery and official government documentation.
Beyond postal routing, this abbreviation carries specific usage rules, historical roots, and alternative meanings that often cause confusion. Knowing how, when, and why to use the code ensures your correspondence and data entries remain accurate.
The Origins of the MD Postal Code
The two-letter code wasn't always the default way to write state names. Before the mid-20th century, longer abbreviations like Md. or Myld. were common in handwritten letters and early print journalism.
The modern iteration came into existence in October 1963, when the United States Postal Service (then the Post Office Department) introduced ZIP codes alongside a standardized list of two-letter state and territory abbreviations.
As mail volume surged following World War II, mechanical sorting equipment required a uniform system. Long state names slowed down processing. Allocating exactly two letters per state allowed sorting machinery and early data entry operators to read addresses at high speeds.
Why Maryland Got MD
Because several states share initial letters, assigning codes required careful coordination to avoid overlap:
- Maine received ME
- Massachusetts received MA
- Michigan received MI
- Minnesota received MN
- Mississippi received MS
- Missouri received MO
- Montana received MT
- Maryland received MD
The letters M and D capture the first and final consonant sound of the word "Maryland," making it a natural fit that remained distinct from neighboring states like Delaware (DE) and Virginia (VA).
Modern Usage Rules in Writing and Addressing
Using the code correctly depends entirely on the medium. Editorial styles and postal guidelines treat the abbreviation differently.
Mailing Addresses and Forms
For envelopes, package labels, and digital database fields, always write the code in all-caps without periods (MD). It belongs on the final address line directly after the city and immediately preceding the ZIP code. For example:
100 State Circle
Annapolis, MD 21401👉 See also: this post
Formal Prose and Journalism
In standard paragraph writing, style guides like the Associated Press Stylebook generally recommend spelling out state names entirely when they stand alone in running text. If you must abbreviate due to space constraints—such as in datelines, tables, or tight charts—traditional styling often favored Md. with a period. However, modern digital habits lean heavily toward the clean, unpunctuated MD format across almost all platforms.
Common Confusions: State vs. Medical vs. Corporate Meanings
The letters MD frequently pop up in entirely different contexts, leading to mix-ups for readers scanning quick text.
In medicine, M.D. (frequently written without periods in modern shorthand as md) stands for Doctor of Medicine, originating from the Latin Medicinae Doctor. Someone holding this degree is a licensed physician.
In corporate governance, MD can also stand for Managing Director, a high-ranking executive title common in finance and corporate leadership firms.
When looking at a geographic database, shipping manifest, or mailing address, context resolves the ambiguity instantly. If a city name precedes it and a ZIP code follows it, it's the state of Maryland.
Frequently Asked Questions
Is there a period in the official postal code for Maryland?
No. The official United States Postal Service standard uses two capital letters with no periods (MD). Adding a period is a relic of older traditional publishing styles.
Why isn't Maryland abbreviated as ML?
When the postal service standardized codes in 1963, they assigned ML to nothing, because combining sounds like M and D was cleaner for rapid visual scanning, and M-end combinations weren't prioritized that way. Furthermore, states like Maine took ME, leaving MD as a logical phonetic choice.
Can I use MD inside a sentence in a formal essay?
It's best to avoid it. Formal academic and journalistic writing usually requires spelling out "Maryland" fully within standard sentences, reserving the short code strictly for addresses, data sets, and charts.
What nickname does Maryland hold that relates to its history?
Maryland is officially known as the Old Line State, a moniker popularized during the Revolutionary War to honor the brave Maryland troops who fought heroically under General George Washington.
