A character mentions buying 'a box seat in Ford's Theatre' - this is a reference to Abraham Lincoln's assassination there in 1865. Following Lincoln's assassination, Ford's Theatre was appropriated by the U.S. government and banned from ever again being used as a place of public amusement. During Grant's presidency, it was in use by the military.
The United States has never honored any of its own treaties signed with any tribe.
The necklace worn by the First Lady will be seen again in season 5 being given as a gift from Gilda St Clair to Colleen for her 17th birthday.
President Grant was talking about the battle of Shiloh.
Dr. Quinn wears the fancy gowns and hats she bought in Boston when she visited her mother and saved her life.