What Is the Abbreviation for Illinois?
The standard abbreviation for Illinois is IL. This page explains why Illinois uses IL, how the code fits into the modern USPS system, what older printed abbreviations looked like, and which nearby or similar state codes people commonly confuse with it.
What Is the Abbreviation for Illinois?
IL is the standard abbreviation for Illinois. Ill. still appears in older print sources, but IL is the standard code used in addresses, forms, databases, and current style guides.
IL is the form used for Illinois in mailing addresses, shipping labels, official forms, and database records.
Why Illinois Uses IL
Illinois uses the USPS abbreviation IL.
USPS has used IL for Illinois since 1963. The older form Ill. still appears in older publications, but IL is the standard postal abbreviation today.
Old Abbreviation for Illinois
Before the USPS two-letter system became the mailing standard in 1963, printed reference books and newspapers often used longer abbreviations with punctuation. For Illinois, that older style was usually Ill..
That older form still appears in historical texts, archival material, and some legacy style guides, but the modern postal and database standard is IL. If someone searches for old abbreviation for Illinois, the practical answer is to recognize Ill. and use IL in current writing and addresses.
How to Write Illinois in an Address
In standard American addressing, the state line uses the city name followed by the two-letter code and ZIP Code. The abbreviation stays uppercase and does not take periods.
That same format applies in checkout forms, school worksheets, CRM exports, spreadsheets, shipping labels, and government databases — anywhere a two-letter state code is required.
IL Compared With Similar State Codes
IL is often checked against ID, IN, and IA because the I-state codes are easy to mix up in forms and alphabetical lists.
Related Abbreviation Questions
These states share a first letter, region, or alphabetical position with Illinois and are commonly checked alongside it.
Capital, Region, and Context
Illinois belongs to the Midwest region. Its capital is Springfield, and its postal code IL is used in addresses, forms, and databases throughout the country.
Illinois entered the Union on December 3, 1818.
FAQ
What is the abbreviation for Illinois?
The standard USPS abbreviation for Illinois is IL.
What is the postal abbreviation for Illinois?
IL is the two-letter postal abbreviation for Illinois. It is the form used in mailing addresses, shipping labels, forms, and databases.
How do you abbreviate Illinois?
Abbreviate Illinois as IL in current USPS, mailing, and database use.
Why is Illinois abbreviated IL?
Illinois uses the USPS abbreviation IL.
What does IL stand for?
IL stands for Illinois in the USPS state abbreviation system.
What is the old abbreviation for Illinois?
Older editorial styles often wrote Illinois as Ill.. For mailing and database use, the modern standard is IL.
How do you write a Illinois mailing address?
Use the city name, then the two-letter postal code IL, then the ZIP Code. For example: Springfield, IL 00000.
What state is IL?
IL is the postal abbreviation for Illinois, located in the Midwest region. The capital is Springfield.
Test All 50 State Abbreviations
Now that you know IL stands for Illinois, see how many of the other 49 you can get right. The M-states and I-states trip up most people.