President Thomas Jefferson chose William Henry Harrison as the governor of the territory, and Vincennes was established as the future capital.

The land containing Putnam County was brought into the possession and control of the United States by the Treaty of St. Mary's in 1818 (known as the New Purchase).

The act tasked five commissioners to meet in May 1822 at the home of James Athey, a log cabin located at the forks of the Eel River.

Records show the court met in session at Athey's cabin in June 1822 and again that September, but the assigned commissioners failed to accomplish their task of selecting a county seat.

An incentive was 70 acres of ground donated for the county seat at Greencastle by Ephraim and Rebecca Dukes, who conveyed the corresponding deed in September 1823.

The terrain of northern Putnam County is mostly flat; rolling hills become more evident in the center and southwest portions.

At the time of settlement, the county was completely tree-covered (poplar, oak, walnut, maple, beech, and hickory),[1] but presently the flat portions have been cleared and used for agriculture; the drainage areas are still wooded.

The highest point in the county (980 feet/300 meters ASL) is a gradual rise two miles (3.2 km) SW of Bainbridge.

[7] Limestone deposits were extracted beginning in the nineteenth century, and a large iron-ore vein southwest of Cloverdale was discovered in the 1860s.

The commissioners execute acts legislated by the council, collect revenue, and manage the county government.

[22] In 1952, Cagles Mill Lake was built as Indiana's first flood−control reservoir, protecting the Eel and White river watersheds.

In 1809, what was left of the great Miami Indian Confederacy sold the now southern one-third of Indiana to the US government, when the 10 O'Clock Treaty Line, which passes through Lieber SRA, was laid out.

[23] The DePauw Nature Park is a 9-mile (14 km) moderately trafficked loop trail that features a lake, wildlife, and bird-watching.

DePauw acquired the adjacent property to increase the total size of the Nature Park to 520 acres (210 ha).

Steep forested sandstone cliffs, lush wooded ravines, and a profusion of ferns and bryophytes characterize the preserve.

[25] Located in Putnam County north-northwest of Greencastle, the 371-acre (150 ha) Glenn Flint Lake is home to a relatively new population of game fish, including panfish.

The Indiana Department of Natural Resources Division of Fish and Wildlife (DFW) manages the fishery at Glenn Flint.

[26] People Pathways is a planning and implementation group established with the approval of the Greencastle Park Board of Commissioners.

The facility is located 35 miles (56 km) west of Indianapolis and is open for club events and professional team testing.