Before beginning your search for industry statistics or demographics, it is helpful to remember these general tips:
Don't Reinvent the Wheel - Often, you do not need to look specifically for statistics. Instead, you may simply need to use the standard library tools (library catalog, research databases, etc.) to help you find good books and articles on your topic—which will usually contain many statistics you can use.
Be Realistic - Be forewarned that no one source may provide all the data you need—you may have to piece together information from several sources. And, in some cases, the best available data may be a few years older or on a different scale (e.g., state level rather than county level) than you desire.
When All Else Fails - Sometimes your only option may be to contact agencies that track the kind of statistics you are seeking. A polite phone call or email often yields surprisingly good results.