Why is LINQ seeing a string element of a text file as an Integer?

I need LINQ to Objects (CSV file) help again, using asp.net; I'm getting an invalid cast (int to string)

I have a CSV file with contents like this (showing first line with headings):

Zip, City, St8, Long, Lat, County
00501,HOLTSVILLE,NY,40.817967,-73.045257,SUFFOLK
00544,HOLTSVILLE,NY,40.8152,-73.0455,SUFFOLK
00601,ADJUNTAS,PR,18.1788,-66.7516,ADJUNTAS
(etc.)

...so I have declared these constants:
  const int ZIP_INDEX = 0;
  const int CITY_INDEX = 1;
  const int ST8_INDEX = 2;
  const int LONGITUDE_INDEX = 3;
  const int LATITUDE_INDEX = 4;
  const int COUNTY_INDEX = 5;

I am trying to query the file using LINQ this way:

    private void FindForCounty()
    {
      RemoveDynamicRows();
      string sCounty = TextBox_Criteria.T ...