This is an important anniversary date for Americans who revere old baseball parks — the Green Cathedrals of nostalgia. April 20 saw the first recognized games played at Boston’s Fenway Park, Detroit’s Tiger Stadium, Chicago’s previously used Wrigley Field, and Baltimore’s Memorial Stadium. The years were 1912 for Boston and Detroit, 1916 for Chicago, and 1950 in Baltimore. Fenway Park and Wrigley Field remain cherished outposts of the national pastime. The Detroit and Baltimore parks were closed in the 1990s and demolished in the first decade of this century. There are 998 professional and semi-pro sports teams and clubs in the U.S., 30 of them are major league baseball clubs, and another 242 are in affiliated or independent minor leagues. Profile America is completing its 18th year as a public service of the U.S. Census Bureau.