In 1790, the first federal population census was taken in the United States. Enumerators were instructed to classify free residents as white or "other." Only the heads of households were identified by name in the federal census until 1850. Native Americans were included among "Other;" in later censuses, they were included as "Free people of color" if they were not living on Indian reservations. Slaves were counted separately from free persons in all the censuses until the Civil War and end of slavery. In later censuses, people of African descent were classified by appearance as mulatto (which recognized visible European ancestry in addition to African) or black.
when did any changes to counting procedures  happen?
until the Civil War and end of slavery.