It's not only one building! Most of LHC ring is in France. The second biggest accelerator, the SPS, is almost entirely in France too. The CERN Control Center,

It's not only one building! Most of LHC ring is in France. The second biggest accelerator, the SPS, is almost entirely in France too. The CERN Control Center, where all accelerators are operated, is in the CERN's site of Prevessin, in France. Out of the four main LHC experiments, three are in France... Still, to simplify we usually say CERN is just in Switzerland. It's somewhat funny (but also convenient) that we use Swiss electricity plugs, and Swiss cell-phone network coverage all over CERN.