On December 12, 2019, the Bureau of Economic Analysis (BEA) released the first official gross domestic product (GDP) by county statistics. This article provides readers with a description of the GDP framework, source data, and methodology used to prepare BEA's official GDP by county estimates. The article is divided into three main sections. The first section explains GDP concepts, definitions, and source data. The next two sections describe the estimation methods used to measure GDP by county, by breaking down the methodology into key components.