What was the document that was the first to ban slavery in a state or territory of the US?

The first document to ban slavery in a state or territory of the United States was the Northwest Ordinance of 1787. This legislation established a framework for governing the Northwest Territory and explicitly prohibited slavery in the region. It was a significant step toward limiting the expansion of slavery in the early United States. The Northwest Ordinance laid the groundwork for future debates about slavery in newly formed states.