Washington Township did not come into being until 1824 when Hendricks County was created. For centuries before this time, it was populated only by roving Indian tribes. The Delaware and Piankishaw Indians used this county as a hunting grounds. There is no record of any permanent Indiana villages, although temporary villages undoubtedly were made while the tribes hunted this land. It was not until the 1600’s that France claimed the vast area of land between Appalachian and Rocky Mountains. It is probable that during that time the first white men, being trappers and explorers, visited what was to be Hendricks County, of which Washington Township is but a small portion; this became English Territory following the French and Indian War of 1763. The area finally became a part of the United act of the United States Continental Congress, the area that now includes the states of Ohio, Illinois, Michigan, Wisconsin and Indiana became the Northwest Territory. In 1800 the Indiana Territory was organized and settlement of the territory by Americans began. The land in the southern part of the state was opened by treaty while Indiana was still a territory. However, it was not until after Indiana became a state in 1816 that the first Governor, Jonathon Jennings, negotiated the treaty of St. Marys in 1818 which opened up for settlement all the area south of the Wabash River. Hendricks County was part of this “New Purchase of 1818”. According to the terms of the treaty, Indians living in the area had three years to remove themselves west of the Mississippi River. The first road was a wilderness road. It was chopped through forests from the Wabash River to Indianapolis.The most important road in this area was built in 1830, and was called the “National Road.”

The National Road was located in the southeast corner of Washington Township. This road was very important because it brought many settlers from the eastern part of the United States. This brought trade and prosperity to this section of the territory. Since there were many settlers coming into the area, every farmhouse became a hotel. In the spring when there was much rain, the roads became impassable with mud. In some instances, the horses would sink to their stomach in this mud. Many of the roads came about by paths of roads made by circuit riders and residents.Two instances of roads made by circuit riders and residents are the roads to Plainfield and Danville which are now State Road #267 and US Highway 36. These roads also became impassable in the spring.

As of the 2010 census, there were 12,446 people, 4,457 households, and 3,384 families residing in the town. The population density was 874.0 inhabitants per square mile (337.5/km2). There were 4,742 housing units at an average density of 333.0 per square mile (128.6/km2). The racial makeup of the town was 86.7% White, 5.9% Black, 0.3% Native American, 3.3% Asian, 0.1% Pacific Islander, 1.4% from other races, and 2.2% from two or more races. Hispanic or Latino of any race were 4.3% of the population. There were 4,457 households of which 45.6% had children under the age of 18 living with them, 62.5% were married couples living together, 9.3% had a female householder with no husband present, 4.1% had a male householder with no wife present, and 24.1% were non-families. 19.4% of all households were made up of individuals and 5.8% had someone living alone who was 65 years of age or older. The average household size was 2.77 and the average family size was 3.20. The median age in the town was 33.9 years. 30.2% of residents were under the age of 18; 6.6% were between the ages of 18 and 24; 31.7% were from 25 to 44; 23.6% were from 45 to 64; and 8% were 65 years of age or older. The gender makeup of the town was 48.3% male and 51.7% female.