Where is localhost folder located in Mac or Mac OS X?

The default Apache root folder (localhost/) is /Library/WebServer/Documents

Also, make sure you have the PHP5 module loaded in /etc/apache2/httpd.conf

LoadModule php5_module libexec/apache2/libphp5.so

There are actually two place where mac os x serves websites by default:

1. /Library/WebServer/Documents --> http://localhost
2. ~/Sites --> http://localhost/~user/