Duncan kan være:
Byer i USA Duncan (Alabama), i Tallapoosa County Duncan (Arizona), i Greenlee County Duncan (Arkansas), i Monroe County Duncan (Colorado), i Saguache County Duncan (Illinois), i Stark County Duncan (Indiana), i Floyd County Duncan (Iowa), i Hancock County Duncan (Kentucky), i Casey County Duncan (Kentucky), i Mercer County Duncan (Mississippi), i Bolivar County Duncan (Missouri), i Webster County Duncan (Montana), i Flathead County Duncan (Nebraska), i Platte County Duncan (Nord-Carolina), i Harnett County Duncan (Oklahoma), i Stephens County Duncan (Oregon), i Umatilla County Duncan (Pennsylvania), i Tioga County Duncan (Sør-Carolina), i Spartanburg County Duncan (Tennessee), i Blount County Duncan (Virginia), i Floyd County Duncan (Washington), i Spokane County Duncan (Vest-Virginia), i Jackson County