Blog — Property Sentinel

One Address, How many PINs?

4/12/2026

Cook County established the Property Index Number (PIN) system, officially known as the Permanent Real Estate Index Number System, in 1946. The modern 14-digit PIN encodes specific geographic information down to the unit:

05-17-417-020-0000
Area-Sub area-Block-Parcel-Unit
New Trier-Section 17-Block 417-Parcel 020-Standard Parcel

The county's official explainer and local lawfirms do a good job explaining the basic PIN facts and relevance for property taxes. Chicago Cityscape, a singular inspiration for this site, does a fantastic job (for a price) at aggregating property details for specific PINs. Property Sentinel is the only place you can type in a Cook County address and get all 311 complaints, property records & characteristics, and public listing details at that entire building—no matter the PIN number, could be none, could be 90—for free.

What Goes Into a Property Page

The Cook County Assessor publishes a number of separate datasets that we ingest on an ongoing, rolling basis. Key among these are the parcel universe (3.7 millions rows covering every parcel in the county), parcel sale history, assessed values, and property characteristics per class. For Chicago addresses specifically, we also have short term rental activity, 311 complaints, violations, and permits. This is only a partial accounting of our data infrastructure—see our Data Sources page for a full list.

The result is a property page that knows a building's latest assessed value (usually two years ahead of the city's own website), an indication if it's over-assessed (tool build in process), a complete set of characteristics, and full picture of listings/complaints/violations/permits.

The PIN Problem

Most addresses map cleanly to one PIN; Kevin McAllister's house at 671 Lincoln Ave is on a single parcel in Winnetka. Chicago's layers of large, old, and renovated buildings complicate this.

Cook County assigns PINs at the parcel level, and parcels follow legal lot lines, not building footprints. A courtyard building constructed on three contiguous lots has three PINs. A mixed-use building with a residential tower and a separate retail parcel has two. A landmark building occupying half a city block may have eight. If the PINs could talk, they'd tell you they're related—sequential PIN numbers at the same block or parcel with the same property tax mailing entity tend to be related—but there's no published record saying "these six PINs are actually the same building."

Take, for example, the historic Monadnock building. Designed by Burnham & Root back in 1891, 53 W Jackson Blvd. is still the tallest load-bearing brick building ever constructed.

The Monadnock Building, two halves built two years apart

Except that's half the story—the other half of the Monadnock was designed by Holabird & Roche and wasn't finished until 1893. That's a second parcel with a separate PIN. It also has 32 other addresses:

300-350 S DEARBORN ST CHICAGO IL 60604
325-325 S FEDERAL ST CHICAGO IL 60604
50-56 W VAN BUREN ST CHICAGO IL 60600
51 W JACKSON BLVD CHICAGO IL 60604

The former is crucial for getting the full picture on property characteristics and taxes; the latter is important for everything else. To my knowledge, Property Sentinel is the only site to do both.

Sibling Pin Matching

Our matching heuristic identifies "sibling" PINs using a few signals in combination: sequential PIN proximity within the same block, shared tax mailing name, consistent property class, and a fourth proprietary method. When a certain combination of the four align, we flag the parcels as siblings and merge their records under a unified building view. Records from all sibling addresses feed into a single timeline, assessed values are summed, and building characteristics are itemized and deduplicated.

Our matching works well for the straightforward cases—courtyard buildings on the North Side, large mixed-use buildings, etc—but it breaks down on edge cases. That's why, when you type in an address for a building with multiple PINs, you're given the opportunity to view the full building or just the solo address.

Hansen 7

Our jigsaw puzzle is still missing an important piece. The city of Chicago maintains a legacy address range database called Hansen 7 that maps every building to its full street address range. It's the reason we know the definitive addresses for the Monadnock and it's also the reason why the neighbor's complaints about the illegal short-term rental in your condo association are lost to the wind. Right now, the only way to query Hansen 7 is through a back door, looking up an address on the city's building records site. Our parent company, City Logical LLC, has filed a FOIA request for the Hansen 7 dataset—if and when that request is granted, it will be freely uploaded to our Github and will complement our sibling PIN heuristic here.

Until we receive the definitive address ranges from the city, we rely on an elegant fallback. If you know your building occupies multiple address ranges—a courtyard building, a large multi-family, a condo association with a parking garage on an adjacent parcel—you can submit those ranges directly from the property page. And if you don't know your building's address range, you can verify it on the city's website. We review every submission against the parcel records and, when confirmed, merge them into a unified building view.

Submitting a building's address ranges manually

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Chicago 311 Complaints: What Building Owners Need to Know

4/1/2026

The Second City logs an average of 1.5 million 311 complaints per year, more than one complaint for every two Chicagoans. Property Sentinel is the only place that tracks complaints by address and sends alerts for what's important. Though building complaints are our primary focus, we also track business and consumer complaints—restaurant inspections, wage violations, tobacco sales, and more. We'll cover those in a future post.

In January 1999, Chicago debuted a centralized 3-1-1 municipal service system to route non-emergency calls away from 9-1-1. Every year since, the city has recorded and responded to over a million complaints a year for everything from building violations to rodent baiting. In December 2018, the city fully modernized the 311 platform by releasing a web and mobile app alongside a free-to-access and comprehensive database. That database is the city's buried treasure—a geocoded catalogue of seven years and counting of citizen interactions with city services. City Logical was founded to make sense of that data; Property Sentinel concerns itself specifically with building-related complaints.

Complaint Types

Each complaint is tagged with a short code that denotes the approximate reason for the complaint: e.g. NAC for No Air Conditioning, CIAC for Coyote Interaction, HFF for Smokeless Tobacco at Sports. There are over 100 codes in total. Information Only Calls (50%) and Aircraft Noise (25%) are the most popular complaints by far and stand apart—no follow-up is required, no enforcement is expected, and no resolution is delivered. The real 311 complaints, about 400,000 per year, generate and demand an appropriate and prompt city response.

Top 10 Complaints from the Last 12 Months (LTM)

Code	Type	Total	Open	Per mo.
311IOC	311 Info Only Call	711,586	0	59,299
AVN	Aircraft Noise	379,643	0	31,637
GRAF	Graffiti Removal	95,118	4,722	7,927
SKA	Abandoned Vehicle	53,158	7,083	4,430
PHF	Pothole in Street	50,726	7,789	4,227
SIE	Garbage Cart Maintenance	50,563	4,379	4,214
SEF	Tree Trim (discontinued)	45,409	6	3,784
SGA	Rodent Baiting/Rat	44,425	2,318	3,702
SFD	Street Light Out	35,679	4,221	2,973
SEL	Tree Debris Clean-Up	29,086	1,637	2,424

Building Complaints

Depending on how you slice it, there is a building complaint reported to Chicago 311 every four and a half minutes. Though some are more serious than others, all require a response from the relevant department: Department of Buildings (DoB) conducts a follow-up inspection for every no permit and plumbing complaint, Department of Water Management (DoWM) investigates basement flooding, and ward-level inspectors check out sanitation code violations. Depending on the circumstances, the inspection may result in a follow-up visit, which may itself require an additional inspection before the complaint is finally closed. As you might imagine, city inspectors are spread thin.

Serious Building Complaints and Response Times LTM

Code	Type	Closed	Median	Lower Quartile	Upper Quartile
BBC	Plumbing Violation	6,911	45.9 days	16.8 days	66.6 days
BBD	No Permit / Construction	2,145	35.8 days	13.7 days	72.8 days
BBA	Building Violation	16,680	16.7 days	3.7 days	50.1 days
SHVR	Shared Housing/STR	489	3.7 days	1.5 days	24.6 days
AAF	Water in Basement	19,243	0.1 days	0.0 days	0.4 days

Water in basement resolves in 2.4 hours. That's not because the city fixes anything, it's because the DoWM dispatches someone to check the sewer, confirms whether it's a city-side or a building-side issue, and closes the ticket. The resolution is a triage, not a repair.

Plumbing violations take 46 days to resolve, nearly three times longer than general building violations, because they require an initial inspection, a licensed plumber to make repairs, and a reinspection to verify. The DoB is the bottleneck on both the initial and reinspection. The upper quartile of 67 days means one in four landlords has an open violation on their record for two months.

Shared housing/vacation rental complaints are handled by Business Affairs & Consumer Protection (BACP) and have a long tail: if you complain about the bachelor party happening at the AirBnB upstairs, the city either warns the host if they're in compliance or conducts an investigation of all the hosts' properties if they're not.

Building complaints are only one piece of the 311 picture. Chicago logged nearly 10,000 business-related complaints in the last 12 months—restaurant complaints, consumer fraud, wage theft, sidewalk café violations—each handled by a different department with its own enforcement timeline. We'll break those down in a separate post.

Staying Compliant

Each building complaint has its own nuances and learning curve. The city only has "a few dozen" building inspectors which means they are reactive by necessity, working through the queue of complaints as they come in, often prioritizing certain buildings and geographies over others. If you're a building owner, finding out about a complaint on the same day it's recorded allows for a quick call to your own plumber—possibly the difference between a quick inspection vs thousands of dollars in fines, or a clean bill of health vs an RLTO violation.

Property Sentinel alerts you to building & business complaints within a half hour of filing. It will also guide you through the complaint-to-resolution window, providing an estimate of inspector response times weighted on recent inspections, weather, time-of-year, and ward-level data. And if you need a recommended tradesman for the job, we're building a network for that too.

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