The Land Ordinance of 1785 was a rule that was made a long time ago, when the United States was still new.
Basically, it was a system to make sure that the land in America was divided up fairly and evenly. People weren't allowed to own or use land unless they had permission from the government.
The government divided up the land into sections that were all the same size, like squares on a table. Each section was one mile long on each side, which is about as long as 16 football fields end to end.
The government also decided how much each section of land would cost, and people had to pay that amount to the government to be allowed to use that land.
This system helped the country grow and develop because it meant that everyone had access to the same amount of land, and the government could keep track of who owned what.