use strict;
use warnings;

my %data;

while (<DATA>)
  {
  my ($id, $location, $info) = /^((?:[^,]*,){2})([^,]*),(.*)$/;
  push @{$data{$location}}, "$id$info"; #Array of user entries for each location
  }

for (sort keys %data)
  {
  print "Location $_:\n  ";
  print join "\n  ", @{$data{$_}};
  print "\n";
  }

__DATA__
Login,Name1,Location1,Info,Info2,Infoblah
Login,Name2,Location1,Info,Info2,Infoblah
Login,Name3,Location2,Info,Info2,Infoblah
Login,Name4,Location2,Info,Info2,Infoblah

##</code><code>##

Location Location1:
  Login,Name1,Info,Info2,Infoblah
  Login,Name2,Info,Info2,Infoblah
Location Location2:
  Login,Name3,Info,Info2,Infoblah
  Login,Name4,Info,Info2,Infoblah