Researchers can use various property tax records from the Board of Assessor’s Office to approximate a building’s construction date by comparing the assessed value of the property from one year to the next and noting the date of an assessment that increases independently of other properties in the square. These records can enable researchers to refine an earlier estimation of a construction date (derived from chain of title research), since the assessments were made every year, whereas several years may have elapsed between the last conveyance of unimproved land the first one with improvements.

Researchers should take care to begin the tax records search in a year when they have confirmed from other sources (such as the Sanborn maps) that the building in question was already standing. Without this confirmation, any conclusions drawn about the significance of changes in the building’s assessed value might be flawed. Begin the research with that year and search backwards, year by year, noting any changes in value that could suggest that a structure was added to the property.