Do I need two ground rods for a 200 amp main in baltimore county?

I am not sure about Baltimore, but there is no 2010 code.

Bottom line is you most likely do need to ground rods for a new service.
If this is a new home then a Ufer (concrete encased electrode) is all you need.

I found these changes adopted :

http://resources.baltimorecountymd.gov/Documents/Permits/ElectricalInspections/2008necupdate.pdf

I found at :

Electrical Inspections Main Page (http://www.baltimorecountymd.gov/Agencies/permits/pdm_elecinspec/)

Does not appear that two rods are required.

Look through it yourself to see if what you have is affected by their changes.