Linq group string array by count and sort

You'll need to use a combination of GroupBy and OrderByDescending:

string[] words = {"Car", "Car", "Car", "Bird", "Sky", "Sky"};
var output = words
    .GroupBy(word => word)
    .OrderByDescending(group => group.Count())   
    .Select(group => group.Key);

You can use GroupBy() then OrderByDescending() to order by number of occurrence starting from the most frequent :

var result = _words.GroupBy(x => x)
                   .OrderByDescending(x => x.Count())
                   .Select(x => x.Key)
                   .ToList();