Is there data on the interstate migration of companies. Including
- Headquarters moving from one state to another
- Employment, by job or broad category, increasing or decreasing by company by state?
I am a student Employee at a state data center. If you are willing to pay for the time, your state data center can gather the data for you, or your state data center can direct you to the source.
As far as employment, it sounds like you want Quarterly Census of Employment and Wages. These numbers are for states/MSA's at the smallest, but also can be all industries. My suggestion is to start at this page http://data.bls.gov/cgi-bin/dsrv?ce and then work your way through the questions, narrowing down to exactly what you want. This site can give you a lot of data.. It's scary.
Then theirs this website, http://onthemap.ces.census.gov/ This a nice mapped interface for looking up places and getting information. If you're looking to get huge amounts of information then you'll likely have to look at county buisness dynamics (i can't post 2 links i guess)
, but this is less intuitive.
Again though, your state data center gets federal funds to make information available to businesses and it would be worth a call/visit!