Emerging evidence supports a link between neighborhood built environment and physical activity. Systematic methodologies for characterizing neighborhood built environment are needed that take advantage of available population information such as Census-level demographics. Based on transportation and urban planning literatures, an integrated index for operationalizing walkability using parcel-level information is proposed. Validity of the walkability index is examined through travel surveys among areas examined in the Neighborhood Quality of Life Study, a study investigating built environment correlates of adults' physical activity.