The Program for the International Assessment of Adult Competencies (PIAAC) is a multicycle survey of adult skills and competencies sponsored by the Organization for Economic Cooperation and Development (OECD). The survey examines a range of basic skills in the information age and assesses these adult skills consistently across participating countries. PIAAC is the sixth of a series of adult skills surveys, sponsored by the National Center for Education Statistics (NCES), that have been implemented in the United States. This third report describes the methodology used to produce the county-level estimates by age and education groups. [For the second report, "Program for the International Assessment of Adult Competencies (PIAAC): State-Level Estimation for Age and Education Groups Methodology Report. NCES 2022-050," see ED622835.]