Fairness in Federal Disaster Declarations Act of 2021 This bill requires the Federal Emergency Management Agency (FEMA) to amend the rules concerning the factors it considers when evaluating a governor's request for a major disaster declaration. FEMA must (1) provide that, with respect to the evaluation of the need for public assistance, specific weighted valuations shall be assigned to the estimated cost of the assistance (10%), localized impacts (40%), insurance coverage in force (10%), hazard mitigation (10%), recent multiple disasters (10%), programs of other federal assistance (10%), and economic circumstances (10%); and (2) consider the economic circumstances of both the local economy of the affected area (including the local assessable tax base and local sales tax, median income, and poverty rate) and the state economy (including the unemployment rate). Such rules are applicable to any disaster for which a governor requested a major disaster declaration and was denied on or after January 1, 2012.