We are working on an interview with Andrei Ivanov, JetBrains Chief Operating Officer, that will likely answer this. For the time being, JetBrains was founded in 2000 in Prague by three software developers: Sergey Dmitriev, Valentin Kipiatkov, Eugene Belyaev. The headquarters and international sales office has remaining in Prague while the company continues to grow.
In total there are 8 JetBrains offices, in addition to remote workers: http://www.jetbrains.com/company/contacts/