8. Utah County, UT

Towns include: American Fork, Lindon, Provo
Job growth (2000-2010): 47.1%

The National Security Agency likes to keep a low profile, but when America`s most secret spy outfit chose Utah County for a massive new cyber-security center, it turned heads -- to the tune of 10,000 construction jobs over the next three years.

It was a natural choice, though: The county straddles a major Internet backbone in Utah`s booming tech hub, and the area`s isolation from the East and West Coasts makes it more secure. When the massive Utah Data Center is completed in 2013, it will occupy one million square feet and employ up to 700 workers.

On a smaller scale, other expansions worthy of mention include IM Flash Technologies, which is adding 200 positions to its Lehi plant, and Overstock.com, which is creating 150 jobs in a new software development center in Provo.

Before:

1. Rockwall County, TX

2. Loudoun County, VA

3. Williamson County, TX

4. Douglas County, CO

5. Hamilton County, IN

6. Delaware County, OH

7. DeSoto County, MS

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9. Ascension Parish, LA

10. Campbell County, WY

11. Livingston Parish, LA

12. Larimer County, CO

13. Prince William County, VA

14. Rutherford County, TN

15. Wake County, NC

16. Williamson County, TN

17. Sarpy County, NE

18. Shelby County, AL

19. Carver County, MN

20. Hendricks County, IN

21. Charleston Country, SC

22. Cache County, UT

23. Madison County, MS

24. Canadian County, OK

25. St. Croix County, WI