Assuming your file format is tab delimited with the fields mm/dd/yy, state num, everything else:

foreach (<MYHANDLE>) {
    $_ =~ /^(\d+)\/(\d+)\/(\d+)\t(\d+)\t/;
    if (!$h{"$1$2$3$4"}) {
        $h{"$1$2$3$4"} = 1;
        $c{$3}{$4}++;
    }
}
foreach $year (sort keys %c) {
    print "$year\n";
    $p = $c{$year};
    foreach (sort {$a <=> $b} keys %$p) {
        print "$_ " . $c{$year}{$_} . "\n";
    }
    print "\n";
}
[download]

MYHANDLE can be replaced with the handle of your flat file after you open it.