what county is wilmington, delaware in
City of Wilmington Department of Finance. 800 North French Street. Wilmington, Delaware 19801. The City of Wilmington City of Wilmington - Tax Assessor & Finance Officer Office is located at 800 North French Street, at the Louis L. Redding City/County Building building in Wilmington, Delaware. City of Wilmington is a locality in New Castle County, Delaware. Unlike many other areas where property taxes are collected on a county level, City of Wilmington has its own tax assessor's office. City of Wilmington