ZIP code 99128 is officially located in the state of Washington, primarily serving the city of Farmington. It falls under the administrative jurisdiction of Whitman County. When planning mail delivery, logistics routing, or demographic research, 99128 operates within the Pacific Time (PT) timezone and supports the 636 area codes.
According to the latest US Census Bureau and American Community Survey (ACS) datasets, the total population residing within the 99128 ZIP Code Tabulation Area is approximately 41,236. Understanding local economics is critical for market analysis; the median household income in this postal area sits at $116,128.