Nature geomaterials like soil and aggregate often exhibit poor engineering properties that make them unsuitable for use in road construction. To overcome this problem, stabilization methods are used to enhance the engineering properties of these materials by mixing them with chemicals. While cement has been the preferred chemical stabilizer for decades, its high cost and environmental concerns have prompted engineers to look for sustainable alternatives. Lignin, a by-product of the paper or biofuel industries, has shown promise as a sustainable alternative to cement for stabilizing geomaterials. Laboratory studies have demonstrated that lignin-treated geomaterials have improved strength capacity and moisture resistance, but these findings need to be validated in the field under local conditions. This study aims to evaluate the long-term field performance of lignin-treated geomaterials used on a granular road in Iowa. A pilot field demonstration site was constructed in 2018 in Buchanan County, Iowa, and a follow-up field evaluation of 4-year duration was executed at the project site. In addition to the lignin product, three proprietary chemical stabilizers and cement were utilized on different road segments for comparison purposes. This study evaluated lightweight deflectometer-derived elastic modulus, dust generation, in situ California bearing ratio (CBR), and roughness. The results showed lignin stabilization to be a viable and effective method for improving the engineering properties of road geomaterials. This study adds to the growing body of evidence supporting the use of lignin as a sustainable alternative to traditional chemical stabilizers in road construction.