People who opposed the Constitution
Their strength was concentrated in rural areas that were underrepresented in some state legislatures, making it more difficult for the people to rise to political action. Back country regions through Maine and Georgia inhabited by farmers and other poor people were generally antifederalists.
They wanted the Constitution to include a bill of rights. Even though the federalists believed a Bill of Rights was unnecessary, but antifederalists were concerned. for example if some rights were protected what could be the objection to providing constitutional protection for others?
They worried that the Constitution did not ensure frequent rotation of office, and over time the elected official would become less concerned with their constituents.