While your property may be in the floodplain, it does not mean that every house requires flood insurance. The flood insurance is based on the elevation of your home. Residents can pay a private firm to conduct a survey and they can appeal to FEMA (not the city). Very few residents were successful in removing their home from the flood insurance requirement, but it is worth a try if you are willing to pay a surveyor.
To find out if your property is already exempt from the flood insurance requirement, check for your address on one of these two FEMA Revalidation Letters. Both documents are located on the City of Dearborn website.