To find historical statistics on the Civil War era, use the following online source:
Historical Statistics of the United States
This is the the standard source for quantitative indicators of American history. It covers dozens of topics (slavery, American Indians, poverty, etc.) and includes 37,000 data series from over 1,000 sources.
IMPORTANT TIP
Tempting as it may be to type in keywords and try to search, that will prove extremely frustrating. You are better off browsing the Table of Contents to identify the most useful tables.