If Webster wrote the first dictionary, where did he find the words?

It would be more appropriate to say he "compiled" the first dictionary. All the words that he included already existed and were being used by people. It's just that before Webster, no one else bothered to sort them alphabetically and print them all into one publication. Webster's job was only to list all the words that were in use at the time, words that can be found in books, letters, newspapers, historical records, etc.