This is some data from Quora and this is number of banks. Each bank have numerous branches so there is 30k Banks times X number of Bank branches. Huge energy consumption :

US has approximately 7K banks and 7K credit unions (Credit unions grow in size and services, shrink in number)

EU has about 9K (Number of European banks decreases rapidly | Business | DW.COM | 21.01.2013)

I would assume that another 3,000 banks from 20 or so countries (Russia (700), Japan (200), China, Canada, UK, Mexico, Indonesia, etc.) with over 100 banks/country.

For the rest of the world I would take Faisal’s estimate - average of 30/country for another 3–4K.

This yields about 30K banks and similar FIs (credit unions, building societies, landesbanken, S&L) globally.