A more precise location at the moment is "in the Berlin area", "Located near the new airport" (BER airport). It's a surprise compared to previous reports/rumors.
The European Gigafactory was promised for quite some time and most recently Tesla said that GF4 will produce Model 3/Y starting in 2021.
Today, Elon Musk revealed that Gigafactory 4 will start from Model Y, which means that Model 3 will still be imported from the U.S., just like Model S/X.
Besides manufacturing vehicles, GF4 will also produce batteries (we don't have confirmation yet whether it means only modules/packs or also cells) and powertrains. In Berlin, Tesla will have also a design center.
Reportedly, around 10,000 new jobs will be created through the investment and Tesla is already seeking employees (see Tesla website here).