Astrodome
The first home run in the Astrodome was by Mickey Mantle.  The pitcher was Turk Farrell.  This was on April 9, 1965 in a game between the Astros and the New York Yankees. The first official home run was hit by Richie Allen of the Philadelphia Phillies in a game on April 12th of that year a 2-0 Astros loss.