How/where can I find out what the frost-line is for my area?
In general you can use these guidelines.





These are very good guidelines that are widely recognized.  However if getting inspected I would just ask your building department for their code requirements.

**NOTE*****  This is how deep your footings would be in undisturbed soil.  So for example if there was a regrading of the land - as often the case in new builds - you would have to go this deep past the disturbed soil or consult an engineer that would sign off on something else.  So if they regraded your land to 3 feet and you lived in Arkansas you would need to go to 54 inches or gets clearance from an engineer to put the footings shallower.