Question: I'm doing research for a professor, but am having some trouble finding the information and data that he needs.  I'm supposed to make a time trend of U.S. land area in square miles -- one with states plus territory and one with just states.  However, I can't find any sources that track the total U.S. land area over time.  Can you help?

Answer: Here's some information for you on square miles of land area broken down by state. The best part about that table is the citation. It cites the Statistical Abstract of the United States. So I went to the StatAb (one of the most amazing series in our collection IMHO ;-)) and found the data going back in time. The StatAb pulls together statistics from across govt into one handy finding aid -- this particular data e.g. is from the decennial census and so we'll be able to find land area at least every 10 years.Searchworks record for the Statistical Abstract of the US. We have holdings in paper going back to 1878 as well as links to several different digital versions. Here for example is page 5 of 1950 StatAb which lists land area broken down into states and regions. 

There's also the US Census quick facts on land area and the US Gazetteer for further reference.