List of counties in Indiana

The U.S. state of Indiana has 92 counties. Each county serves as the local level of government within its borders. Although Indiana was organized into the United States since the Northwest Ordinance in 1787, its land was not always available for settlement. Eventually, land was purchased from Native Americans by treaties and Indian removals. The oldest counties are generally in the south near the Ohio River, whereas newer ones were in the north in territory acquired later. The oldest and newest counties in Indiana are Knox County, created in 1790, and Newton County, created in 1859.

As of the 2000 United States Census, the population of Indiana was 6,045,485, the average population of Indiana's 92 counties is 65,712, with Marion County as the most populous (903,393), and Ohio County (5,623) the least. 54 counties have 30,000 or more people; 16 counties have populations exceeding 100,000, five of which exceed 250,000; and only five counties have fewer than 10,000 people. The average land area is 396 square miles (1,030 km²). The largest county is Allen (657 sq. mi., 1,702 km²) and the smallest is Ohio (86 sq. mi., 223 km²). According to the Constitution of Indiana, no county may be created of less than 400 square miles (1,000 km²), nor may any county smaller than this be further reduced in size.

County government in Indiana consists of two bodies, the county council and the commissioners.

Many Indiana counties are named for United States Founding Fathers and personalities of the American Revolutionary War, the War of 1812 and Battle of Tippecanoe; early leaders of Indiana Territory and Indiana, as well as surrounding states like Michigan and Kentucky; plus Native American tribes and geographical features.

The Federal Information Processing Standard (FIPS) code, which is used by the United States government to uniquely identify states and counties, is provided with each entry. Indiana's code is 18, which when combined with any county code would be written as 18XXX. The FIPS code for each county links to census data for that county.

In Indiana, the most commonly seen number associated with counties is the state county code, which is a sequential number based on the alphabetical order of the county. It has been used on automobile license plates since 1963. It first held a prominent place on the left side of the plates as part of the license plate number until the year 2008 when it was moved above the serial number and 2012 when it was moved to the lower right corner. On license plate numbers, county codes 93, 95, and 97-99 were also used for Marion County in addition to 49. 94 and 96 were used for Lake County in addition to 45.