Most marketing platforms charge you for audience data that's already publicly available. The U.S. Census Bureau, the American Community Survey, and various state data portals contain incredibly detailed demographic and geographic information — and it's all free.
In this walkthrough, I'll show you exactly how I built the audience estimation engine for the Marketing Planner tool, what data sources I used, and how you can apply the same approach to your own campaigns.
The Data Sources
The Census Bureau provides several APIs that are directly useful for marketing geo-targeting. The key ones I used are the American Community Survey (ACS) 5-Year Estimates and the Population Estimates Program (PEP).
Building the API
The Marketing Planner API takes a ZIP code, platform preference, and optional demographic filters, then returns an estimated audience size with a confidence range. Here's how the logic works at a high level.
What I'd Do Differently
If I were starting this project over, I'd invest more upfront time in caching strategies. The Census API has rate limits, and the real-time query approach I started with doesn't scale well. A nightly sync with a local SQLite database would have saved me a lot of debugging headaches.