I recently read about a proposed affordable housing development in the Chicago suburbs that invoked the Area Median Income for the region:

According to a memo, The Residences at River Point would set aside one-quarter of the apartments for households making 30% or less of the area median income. Roughly half would be earmarked for households making 60% or less of the AMI, and the rest would be for those making 80% or less of the AMI.

According to the federal Housing and Urban Development Department, the AMI for the Chicago metropolitan area, which includes Kane County, is $50,976 for a four-person household.

The AMI is set by HUD who has a chart of the various cutoff points for the AMI for the entire region. From the City of Chicago:

For those who have not run into these figures before, several things from this chart might stand out:

1. The AMI depends on household size. Discussions of housing and affordability can often focus on median household incomes but HUD adjusts for the total number of people in the household. This fits with housing with more space and bedrooms generally being more expensive.
2. The AMI figures are for an entire region. The Chicago region includes more than 9 million residents and hundreds of municipalities. While the AMI limits for Chicago might differ quite a bit from other regions, there can be quite a bit of variation within the region as well regarding incomes and housing prices.
3. These income guidelines apply to a number of programs but are not the only metrics that might be used regarding housing affordability.