We have checked the dictionary,

we put it into spell check and the

answer is definitive.  The plural of chimney is chimneys.  And here in Jacksonville, FL right in the heart of the South many people call it a chimiley.  We don't know why, but we feel pretty safe saying that it's plural would be chimileys.  Whatever you call it, however you spell it, be sure you have a chimney sweep clean your chimney every year.