From I-75, take Exit 263 (South Marietta Parkway). Go west past Southern Polytechnic State University. Go under the Railroad tracks and turn left onto Powder Springs Street. (There's a CVS on the opposite corner.)
You'll take Powder Springs Street halfway across Cobb County, then do one of two things:
Either turn right on West Cobb Parkway, then immediately left onto Macedonia Road. The park will be on your right a mile or so later. ...
OR, if you pass West Cobb Parkway, you can turn right a few miles later onto New Macland Road (highway 176). Then you'll turn right onto Macedonia Road and the park will be on your left.