I don't understand why you want to use a regular expression instead of a simple equality operator. Because $county is a number, however, you should be using == instead of eq.

To add up all the totals, simply declare a variable outside your loop and add each one.

my $total = 0;
while( my $line = <$FhIn> ) {                             
    my ($county, $year, $yr_tot) = split ' ', $line;      
      if ( $county == 26005 )  {                          
          print "$county  : $yr_tot\n";     
          $total += $yr_tot;                     
    }                                                         
}
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