How to research a house in Philadelphia
OpenDataPhilly's parcel data, the Department of Records deed search, the Free Library and the Philadelphia City Archives, the famous Hexamer insurance surveys, Sanborn maps, and the census — how to trace a Philadelphia rowhouse back to the colonial grid.
By The Plot Team · May 29, 2026 · 4 min read
Philadelphia is one of the oldest and best-documented cities in America, laid out on William Penn's grid in 1682 and recording itself ever since. A Society Hill colonial, a Fishtown trinity, a West Philly Victorian twin, a row of Northeast porch-fronts: the trail for each runs deep, and a good part of it is free. Here's how to work the Philadelphia record.
Start with the parcel: OpenDataPhilly
Philadelphia consolidates city and county government, which simplifies your research. The city's open-data platform, OpenDataPhilly, publishes parcel data through the Office of Property Assessment (OPA) — keyed to an OPA account number — with the address, the year built, the building category, and characteristics. The Atlas property tool (atlas.phila.gov) is the friendly front door: type an address and you get the OPA record, the deed history index, zoning, permits, and even nearby historical imagery in one place. This is the strongest free starting point of any American city, and the parcel layer is exactly the kind Plot reads.
Trace ownership: the Department of Records
Deeds are recorded by the city's Department of Records, searchable online through its epay records system (epay.phila-records.com) and surfaced in Atlas's deed history. Be realistic: it's a search-and-order portal with per-document fees, not a bulk feed. Atlas will show you the recent chain by index; for the document images and the older chain you order through the Department of Records or consult the City Archives. Read the chain oldest-first to see who built, who bought, and how the house passed hands.
A Philadelphia specialty: the Hexamer surveys
Before you reach for Sanborn, know that Philadelphia has something rarer. The Hexamer General Surveys (Ernest Hexamer, 1866–1896) were detailed fire-insurance surveys of Philadelphia's industrial and commercial properties — factories, mills, breweries, refineries — drawn building by building with construction, machinery, and use annotated. The Free Library of Philadelphia has digitized them and put them online free. If your building was once industrial or sits near a mill, the Hexamer survey can be astonishingly detailed.
See the block: Sanborn and atlas maps
For residential blocks, the Sanborn fire-insurance maps (free through the Library of Congress) show your row footprint by footprint, color-coded by material, across editions. Philadelphia is also exceptionally well served by 19th-century real-estate atlases — the G.M. Hopkins and Bromley atlases, many digitized through the Free Library's "Greater Philadelphia GeoHistory Network" — which print owner names and lot lines and let you overlay the historic city on the modern one. The GeoHistory Network is one of the best free city-history map portals in the country.
Find the people: census and directories
The federal census (public 1850–1950) names everyone in the household — essential in a city shaped by Irish, German, Italian, Jewish, and the Great Migration's Black newcomers. The Philadelphia city directories (McElroy's and Gopsill's), many digitized on the Internet Archive and held at the Free Library, fill the years between counts. Philadelphia is also the home of the Historical Society of Pennsylvania and the Library Company of Philadelphia (founded by Franklin), two of the deepest research collections in the country.
The Philadelphia City Archives
For the documents that aren't online, the Philadelphia City Archives holds the deep municipal record — building permits, water and gas connection records (a clever way to date a house, since service was hooked up when it was built), tax assessments, and the older deed books. It's the room where a Philadelphia house history reaches back toward Penn's grid.
Landmark status
Check whether your house is on the Philadelphia Register of Historic Places (the city's Historical Commission keeps it, and designation can protect the exterior) or the National Register. Philadelphia has many local historic districts — Society Hill, Old City, Rittenhouse–Fitler, and others — whose nominations contain ready-made block histories.
Let Plot assemble the Philadelphia record
Plot resolves a Philadelphia address against the city's open parcel data and the broad public record automatically — the year built, the lot, the press, archival imagery — and writes a cited history. For the deed chain, Plot points you to the Department of Records / Atlas search and the City Archives — the parts the city keeps in its own portals — while it gathers everything else for you.