<em>Dreamt</em> is more common in British English than in American English, but according to <em>http://grammarist.com/usage/dreamed-dreamt/</em>; both Americans and Brits use it.  As a native British English speaker I often use 'dreamt'.  Both dreamed and dreamt are correct. 

You can find dreamed and dreamt in the dictionary. Most people I've heard say dreamed though.

Americans use both dreamed and dreamt.

Personally I say 'dreamt' (pronounced 'dremt') but 'dreamed' is equally correct.

Thanks Susan!