Generally, since the county assessor appraises at what is usually significantly below FMV, the IRS frowns on that. But, if you have absolutely no other source to determine it's FMV when placed in service, then you have no choice. One question the IRS may have is this: "Why are you reporting this FMV for depreciation 4 years after it was placed in service?" (Can you say "possible audit?")
