How to compare a list and a text file using C#

1.In place of your list and counts you could create a class that contains two properties: StringForSearch and Occurrence (counter) then you could create the List of this object types;

2.For reading the file you could use StreamReader to read line by line like in the next example

using (StreamReader reader = new StreamReader("file.txt"))
{
            string line;
	    while ((line = reader.ReadLine()) != null)
	    {
		CompareLine(line, listOfStrings);
	    }
}

3.For comparing just pass the line read above to a method that use the list from the 1st point to search your initial text and to increment the counters for matching.