Patrick,
you're right about C.B. Macdonald's work at Chicago. The original site of the Chicago GC was in Belmont, Il., and was the USA's FIRST 18-HOLE COURSE (9 holes designed by Macdonald). in 1895, the club moved to Wheaton, Il., where Macdonald designed all 18-holes. however, older courses did exist in the USA, namely the four other charter members of the USGA besides Chicago GC, St.Andrews GC in Yonkers-on-Hudson, NY., Shinnecock Hills GC in Southampton, NY., The Country Club in Brookline, Mass., and the Newport GC in Newport, R.I.
the Newport & Shinnecock GC's were designed by William Davis originally, in 1894 & 1895 respectively. Newport being 9 holes, and Shinnecock being 12. The Country Club was designed by Willie Campbell in 1893 as a 9-hole course.