Determining where to find the geographic center of the EU comes with different challenges. First, you have to eliminate countries that are no EU member countries, such as Switzerland, from your calculation. Second, the center changes every time the EU gains new members or loses some.
The Geographical Institute of France (IGN) has been documenting the center of the EU as well as its shifts since 1987. This interactive dashboard shows how the center has moved with every expansion of the EU.
After Spain and Portugal joined the EU in 1986, the geographical center could be found in Saint-André-le-Coq, a small community in the region of Auvergne in France. As soon as Germany was reunited again the heart of the EU shifted 33 km to the east.
In 1995 Austria, Sweden and Finland joined the European Union. That led to a repositioning of the center by 445 km. A small community in the Belgian province Namur called Viroinval, could only claim the title as most central place for five years.
The expansion of the EU in 2004 by ten mostly eastern states moved the center to Kleinmanscheid in the Westerwald in Germany. But only three years later Kleinmanscheid had to hand over the title to Gelnhausen in Hesse, Germany, because of the entry of Romania and Bulgaria to the EU.
When Croatia joined the EU in 2013 it pushed the center only 9 km further, to Westerngrund in Bavaria.
Even the addition of the French overseas department Mayotte, which can be found off of the coast of Madagascar, did not change the fact of Westerngrund holding the title. However, the Exit of Great Britain would move the geographical center to an acre in Gadheim, yet remaining in Bavaria, Germany.