You can consider doing a search by location, but here is an old, neat trick to know the approximate number of people in any geographic area/profession: Use "Advertise with LinkedIn" and proceed with geographic segmentation.
I tried this out, and the result comes out to be a little over 2.5 MM. (See screenshot below)
If you reach this screen, scroll down to select job titles and then, start selecting different job functions. You will see the numbers for each job function. Some prominent functions:
- Consulting: 77.5K
- Marketing 77.8 K
- Legal 49.6 K
- Finance 85K
- Engineering 209 K (Is anyone surprised?)
- Entrepreneurship 217.6 K (For this one, even I am surprised, but perhaps, only in Bay Area, Entrepreneurship can be a leading job function!!)
Hope this helps!
See question on Quora