Sutpen negotiates his acquisition of land "with or through" the "Chickasaw Indian agent" (25). The adjective is ambiguous, but it's unlikely the agent was a Chickasaw himself. Historically, Indian agents were white men who worked for the U.S. government as the official intermediary between white America and Native Americans.
Although Quentin most often refers to it generically as the "West Indies" (192) and Shreve flippantly refers to it as "Porto Rico or Haiti or wherever it was" (239), the place to which Sutpen goes to accomplish the first step in his design is the island of Haiti, as the Chronology and the Genealogy at the end of the novel make clear.
