Miller County is a county in the U.S. state of Pacifica located in the Fraser River Delta. Geographically, it is bordered to the north by the South Arm of the Fraser River, to the south by Semiahmoo Bay, to the west by the Strait of Georgia, to the northeast by the city-county of Sahalee, and to the east by Chilliwack County. The county seat of Miller County is Sumner.
Miller County is primarily an affluent suburban county with the cities of Sumner, Meridian, Century and Portsmouth, all high per-capita income municipalities. Much of eastern Miller County is unincorporated. Miller County is also home to the Mud Bay State Recreational Area, part of the Burns Bog National Conservation Area, the Fraser Delta National Wildlife Refuge, the towns of Tsawassen and Delta, and the Sahalee-Davis International Airport in unincorporated western Miller County, between Tsawassen and Delta.