1800 Census

In addition to the state and county, the following categories were included:
[1] head of household
[2] number of free white males and females in age categories - 0-10, 10-16, 16-26, 26-45, 45 & older
[3] number of other free persons, except Indians, not taxed
[4] number of slaves
[5] town or district of residence

Surviving 1800 schedules: SC, NC, VA, PA, NY, CT, MA, NH, VT, MD, DE, RI, ME [part of MA]

Lost schedules: GA, Indiana Territory [IN], KY, Mississippi Territory [MS], NJ, Northwest Territory, VA, Tennessee [TN], Alexandria Co., District of Columbia [Some schedules have been reconstructed.]

Each column under the age groups was marked with the number of people who fit into that category. It was often the case that the "tick" marks were written in the wrong columns. That is something to be aware of.  If your ancestor was, say, 25 [16-26], he or she might have been inadvertently marked in the [26-45] column. If that is the only "age group" error in the census for your family, you may still have the right one.