(From Wikipedia): The Land Ordinance of 1785 was adopted by the United States Congress on May 20, 1785. Under the Articles of Confederation, Congress did not have the power to raise revenue by direct taxation of the inhabitants of the United States. Therefore, the immediate goal of the ordinance was to raise money through the sale of land in the largely unmapped territory west of the original states acquired at the 1783 Treaty of Paris after the end of the Revolutionary War. Over three-fourths of the area of the continental United States ultimately came under the rectangular survey. This was important because it provided easily recognized land descriptions, which in turn contributed enormously to the orderly and largely peaceful occupation of the land. The rectangular survey also provided the units within which economic, political, and social development took place.
Above is a map of Indiana from the land survey. More on the Land Ordinance’s impact in Indiana can be found here.