Hancock County was created on March 1, 1828, and named for John Hancock, the first signer of the Declaration of Independence. The town of Greenfield was chosen as the county seat on April 11, 1828. The Commissioners announced, "The seat of Justice of Hancock County shall be known and designated by the name and title of Greenfield." The population of the county at that time was 400.

In 1833, the Indiana Gazetteer published, "Greenfield is surrounded by a body of rich, fertile land and is in a very prosperous and flourishing state of improvement."

Early settlers built along the two creeks which flow south through Center Township, which includes Greenfield. The first businesses were small grist mills for grinding corn and wheat for settlers.

U.S. 40, the National Road, was built through Hancock County around 1835. It was heavily traveled by wagon trains going west and livestock going to Cincinnati. In 1853, the first steam railroad was completed by the Indiana Central Railroad at the south edge of Greenfield. The railroad became part of the Pennsylvania Railroad System and later the Penn-Central. These tracks were removed in the 1980s.

During this time, Greenfield's population continued to grow. Greenfield was incorporated as a city in 1876 with a population of 2,023 (click here for a list of Greenfield's past mayors since incorporation). The greatest single period of growth began in 1887 when natural gas was discovered in the area. Greenfield was a boom town for 20 years, with the founding of manufacturing plants and other industries.

In some earlier historical publications, "Hancock County has been described as within the genius belt of Indiana." It was also said that "here oratory flourishes and the poetry is indigenous to the soil." Among the greats of the city were James Whitcomb Riley, the "Hoosier Poet"; two famous artists, Will Vawter and Dick Black, Earl K. Smith, composer of "Down by the Old Mill Stream", and Rev. Charles O'Donnell, later President of Notre Dame.

A statue of James Whitcomb Riley, which stands in front of the Hancock County Courthouse, was erected in 1918. It was purchased with money donated by school children from all over the United States. Each year, during the Riley Festival in October, the city's school children parade to the statue to place flowers around it.

Today, Greenfield represents the best of both worlds blending its small-town atmosphere with managed growth as part of the greater Indianapolis metropolitan area.  The population of Greenfield, 14,600 in the 2000 census, has continued to grow steadily due to the fact that Hancock County is the sixth fastest growing county in the state of Indiana.

In a letter to Helen Downing, James Whitcomb Riley described Greenfield as "My home and your home and your parents' home and the best home outside of heaven."