Census maps of population: Population over Time and Distribution of slaves in 1860.
Through the Decades section: This section includes lesson plans, maps, classroom resources, and games.
Fast Facts give paint a picture of the United States both statistically and culturally.
Great reference tool Barb! I like the "Through the Decades" Fast Facts section, this would be a great extension activity for kids that are history buffs and like to collect this kind of detail.