Locate Git installation folder on Mac OS X

simply type in which git in your terminal window and it will show you exactly where it was installed.

Is it in your PATH? If so just run which git in the terminal and it will tell you.

The installer from the git homepage installs into /usr/local/git by default. See also this answer. However, if you install XCode4, it will install a git version in /usr/bin. To ensure you can easily upgrade from the website and use the latest git version, edit either your profile information to place /usr/local/git/bin before /usr/bin in the $PATH or edit /etc/paths and insert /usr/local/git/bin as the first entry (see this answer).