Government Information: Finding Historical Statistics

There are sources of historical statistics

1. Compiled volumes, published as secondary sources that record historical data. An example is Cambridge's Historical Statistics of the United States
2. Compiled volumes, published during the historical period being studied (in the 19th century, sometimes called "blue books" or almanacs). A example are Census reports, like this 1850 Census study of Oregon Territory.
3. Contemporary reports (primary sources) published by authors or organizations, such as the USDA Annual Report Animal Usage. These contain bits of important data that you can piece together.
4. Collected data in published secondary books or articles. An example would be an article in which the author(s) consulted local archival records and compiled data for themselves. An example is Allen's "On the Mammals of Aransas County, Texas, With Descriptions of New Forms of Lepus and Oryzomys," in which archival materials were consulted to determine the number of camels in Texas in 1855.
5. Archival materials, such as contemporary organization minutes/records. An example may be minutes, records, or letters of American Humane members in 1880.

Generally speaking, it is best to begin with a review of published (secondary) materials first to determine whether the data you need has already been compiled. Citations in published studies will also tell you were to look for statistics. Finding raw statistical data in primary sources can be difficult and time consuming, and accessing statistical information in restricted archival material can be extremely challenging (and sometimes impossible).

I'm interested in the use of Camels in the US military before the Civil War. First, I look for Secondary Sources in the PSU Catalog and find several books, one of which is even a primary source.

I also want to look in America: History and Life and search Camels AND History. I find a number of additional interesting articles on my topic.

Some of these published works, such as this article, contain statistics I can use.

Others, like Allen's work, points to a potentially useful primary source: Reports upon the Purchase, Importations and use of Camels and Dromedaries, to be Employed for Military Purposes. 1857. Like many 19th century publications, I was able to find a free copy on HathiTrust. This primary source also contained compiled statistics:

It also has excellent images of camels.

I also looked in published compiled volumes, but did not find anything camel specific. Using Google advanced search to search the US census, I found reference to Camels in the 1860 Census, but no statistical data. 

Overall, my best bet is collect statistical information from the sources I've already identified, and use them to write my Camel-themed masterpiece: