 Certain officials, such as the sheriff and tax collector, are elected separately by the voters, but the commissioners' court determines their office budgets, and sets overall county policy.All county elections are partisan; the one exception is the board of trustees of the Dallas County department of education (the Harris County trustees were elected on a nonpartisan basis until 1984).While the counties have eminent domain power and control all unincorporated land within their boundaries, they have neither home-rule authority nor zoning power.