We use the death rate within confidence intervals weighted by populations to extrapolate a range: ~2% - ~6%. So, with that, if there are 5 deaths in your state, we assume 83 to 250 cases.
But the virus takes an average of 17.3 days to kill people, and has a doubling rate of 4 to 6 days. For reference that gives us a huge range of 612 - 5011 within that state, both of which are orders of magnitude above reported cases.