The responses thus far have given you a good starting point. The complete answer is "it depends." If you are NOT obtaining a loan and have no intention of doing so, then flood insurance is NOT required (although certainly not a smart move to avoid Flood Insurance blindly).
However, presuming you intend to finance the property now (or at some time in the future), the requirement for Flood Insurance will be determined by the lender/lien holder/investor requirements.
It is true that FEMA maps may change from time to time. However, just because the lot is currently in the flood plain does not mean you will have to have flood insurance, so don't despair.
You may hire a Surveyor, as noted by Mr. Colvin, and request a current Field Elevation Certification. The Surveyor should note the elevation of the flood plain, the foundation, as well as the 1st floor elevation.
From my 25+ years of experience, I have found that if the house in on a crawl space or slab, and the 1st floor elevation rests entirely above the flood plain, then FI will not likely be required. However, if there is liveable space in a basement, the basement floor will most likely have to rest above the flood plain.
Caution: Different investors have different requirements. So consult with your lender to discern their investor requirements, and don't assume that all lender's requirements will be the same.
Merry Ann Cutler/REMAX United MerryAnn@MerryAmm.com