String[] index number from regex search

Question

I have a string[] that I search using regex and it returns a list of elements in my string[] that match what I searched for using regex. I would like to find the index number of the elements that are returned.

example:

string[] StringArray = {"aaa","bbb","ccc","ddd","eee"};

string find = "bbb";


                            List<string> FoundList = new List<string>();


                            foreach (string Block in StringArray)
                            {
                                if (System.Text.RegularExpressions.Regex.IsMatch(Block, find,
                                                                                            System.Text.RegularExpressions.RegexOptions.IgnoreCase))
                                {
                                    FoundList.Add(Block);
                                }
                                else
                                {
                                    //do nothing
                                }
                            }


                            string[] FoundArray = FoundList.ToArray();


it will create FoundArray = {"bbb"} and I wish to find int i such that 

StringArray[i] = FoundArray[0] 

is true and for senarios where FoundArray has multiple entries I plan to loop it. Any help would be much appreciated.