Riiiight. I've stood in two counties at the same time everytime I've hiked across the Continental Divide in Wyoming.
I hope to visit Wyoming one day . . . should the Lord tarry.
I was thinking municipality, rather than a physical mountain, but even then it would be a Maryland-only thing at best. Lots of cities are split between one or more counties. (Atlanta 2, Dallas 3 or 4, (Actually quite common in the Dallas area- Richardson, Plano, Frisco, Grand Prairie, Sache, Wylie, Trophy Club, Rowlett, Seagoville are all multi-county.) )