There were several known Gist Settlements in Ohio. You mention Highland County, Ohio, have you looked into Adams, Brown & Erie counties as well?
From Ohio History Connection/Ohio History Central:
"Many of Gist's former slaves, perhaps as many as 150 people, remained in Virginia, living on their former master's land. Perhaps as many as 350 other former slaves moved to Ohio, where they established several communities. These communities are commonly known as Gist Settlements. The first of these settlements was located in Erie County. The first Gist slaves may have arrived here in the late 1820s or early 1830s. After several years, they abandoned this settlement, probably due to the poor quality of land, and returned to Virginia. The executors of Gist's estate eventually purchased approximately two thousand acres of land in Adams, Brown, and Highland Counties. The Gist Settlements in these three counties survived into the twentieth century. At the start of the twenty-first century, descendents of the former Gist slaves still occupied part of the land in Highland County. From the 1840s to the 1920s, an average of 150 people resided in each of these communities. Most residents were farmers."