County adjacent to Indianapolis-Marion County on the south and part of the Indianapolis Metropolitan Statistical Area. In 1818 Jacob Whetzel determined to blaze a trail from Franklin County to Greene County, but settled instead on the bluffs of White River in what is now Johnson County. This trail, known as Whetzel's Trace, was used by many early settlers of Marion, Johnson, Morgan, and Shelby counties.

Johnson County was organized in 1822. Whetzel's Trace, the Ancient River Trail, and the Madison and Indianapolis State Road all facilitated settlement of the county, which was traversed by the White and Blue rivers and Sugar Creek. A site for the county seat was chosen near the geographic center of the county, with the town of Franklin platted there in 1823. It grew rapidly and was incorporated as a city with over 2,000 residents by the time of the Civil War.

The second important town in early Johnson County was Edinburgh. Platted in southern Johnson County in 1825, Edinburgh grew slowly until the MADISON AND INDIANAPOLIS RAILROAD was completed there in 1845. The population quickly doubled and Edinburgh became the leading grain and pork market in central Indiana, with merchants coming from as far away as Danville, Spencer, and Bloomington. Edinburgh's growth slowed with the completion of the Madison and Indianapolis Railroad to Indianapolis in 1847, but it continued to be the manufacturing center of the county throughout the 19th century.

Before the railroad arrived, Johnson County was served by a stagecoach line that ran from the capital to Madison along the Madison and Indianapolis State Road. Taverns were constructed in the county at five-mile intervals along the route to serve travelers and provide fresh horses. The coach was abandoned in the late 1840s.

In 1835 the Indiana Baptist Education Society founded the Indiana Baptist Manual Labor Institute at Franklin. The IBES operated the institution until May, 1872, when it declared bankruptcy. During the summer of that year the Franklin College Association, a group of local residents who wanted to save the school, assumed the institutes debts and managed to reopen it in September. The name was officially changed to Franklin College, and the Franklin College Association operated it successfully until 1907 when it was incorporated as Franklin College of Indiana. As of 1993 Franklin College is recognized throughout the state and the Midwest as an excellent small liberal arts college.

The town of Greenwood was established in northern Johnson County in 1864. It had a population of around 350 for many years, but grew rapidly with the completion of the electric railway from Indianapolis in 1900. By 1902 Greenwood, Franklin, and Edinburgh were all connected to Indianapolis by INTERURBANS, and all were prosperous towns.

The demise of the RAILROADS and interurbans crippled Edinburgh. Already replaced as a market, the town lost its industry as well. Its population has declined since 1970 even though the population of Johnson County increased by over 25,000 during the same period. Franklin, with a 1990 population of 12,907, has remained a successful small college city.

Greenwood, a city of 11,869 in 1970, has far outstripped its former rivals in recent years. The growth of Indianapolis has led to much suburban residential and commercial development along U.S. 31 in Greenwood, including Greenwood Park Mall, the largest shopping center in the Indianapolis area. In 1990 Greenwood had a population of 26,265.