To our knowledge, we describe the earliest confirmed detection of HCV infection in the United States. Because the recruits were obviously not interviewed for potential risk factors, the sources of infection cannot be determined. Our results suggest that a low rate of HCV infection has been present in the United States for the past five decades, especially in military populations. Presumably, the rate in the general population began to increase in the 1960s along with parenteral drug abuse; this may account for the higher prevalence of HCV infection found in NHANES III. It is unknown why more African-American Air Force trainees than white Air Force trainees in our study were positive for HCV; however, this trend has also been seen in the recent NHANES III study. Also of note, all but 1 of the 11 persons in whom HCV RNA was detected were characterized as having genotype 1b; the remaining person could not be genotyped. This frequency of genotype 1b is higher than that currently found in the United States and other western countries (34). Although the reason for this prevalence is unknown, presumably genotype 1b was the predominant genotype when the original studies were conducted.

Gina Kolata followed up with Dr. Seeff (now at NIH) in a 2000 NYT article about the Wyoming HCV AF survivors.  http://www.nytimes.com/2000/04/11/science/old-blood-samples-offer-new-clues-to-a-medical-mystery.html?pagewanted=all&src=pm

From what I’ve been reading, HCV probably entered the Caribbean and US during the slave trade but it was transmitted inefficiently.