First of all, you don't need to get the file size. Leave the read size unwired and it will read the entire file. Also make sure to close the file.
Ok, let's take this 1 step at a time. First you want to get an array of the county data. Since the counties are separated by a blank line, you should use the Spreadsheet String to Array with two end of line characters as the delimiter (put string constant in \ display mode and use "\n\n").
So now we have to figure out how to parse the county data. Use the Spreadsheet String to Array function again, this time with a single end of line character as the delimiter. This separates the county data into lines. The first line is the county name, second the largest city. Run the rest of the array into a FOR loop, parse the string with a tab as the delimiter, and build you cluster.
Clear as mud? If you take it 1 step at a time, it is not that bad.
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