An Okie is a resident or native of Oklahoma

An Okie is a resident or native of Oklahoma. Like most terms that disparage specific groups, it was applied by the dominant cultural group.^[1] It is derived from the name of the state, similar to Texan or Tex for someone from Texas, or Arkie or Arkansawyer for a native of Arkansas.

In the 1930s in California, the term (often used in contempt) came to refer to very poor migrants from Oklahoma (and nearby states). TheDust Bowl, and the "Okie" migration of the 1930s brought in over a million newly displaced people; many headed to the farm labor jobs advertised in California's Central Valley.

Dunbar-Ortiz (1996) argues that 'Okie' denotes much more than being from Oklahoma. By 1950, four million individuals, or one quarter of all persons born in Oklahoma, Texas, Arkansas, or Missouri, lived outside the region, primarily in the West. 

Source: Wikipedia