Assuming that you mean ground forces not air forces ...

Germany

No, the first US soldiers to cross into Germany appears to have been a patrol from the 85th Reconnaissance Squadron who crossed the Our river on September 11th 1944.

Europe

Yes. US troops landed in Sicily on July 10th 1943 and followed up the capture of that island with an invasion at Salerno on the Italian mainland on September 9th. Allied forces then advanced up the peninsula for the remainder of the war. Rome was captured on June 4th 1944, two days before the D-Day landings.

Also the US Office of Strategic Services (the indirect fore-runner of the CIA) ran a number of spying operations within Nazi occupied Europe.