It's part of a special census effort aimed at recovering federal funding the city says it lost following the 2020 census.
Each letter contains a unique code tied to a specific household and allows residents to complete the survey online.
"As soon as you get those we just wan to go to your phone, your tablet, your computer and fill it out right away and then you don't have to worry about it anymore," Aurora Chief of Staff Shannon Cameron said.
City officials said the recount is being conducted because the 2020 U.S. Census showed Aurora losing about 17,000 residents.
Since then, the city has lost $4.3 million annually in federal funding, according to officials.
"We haven't lost any population. If anything we have gained significantly," Mayor John Laesch said.
Laesch said the reduced population count has had significant financial consequences for the city.
"Our police and fire staffing levels are all determined by that population count," Laesch said. He added that "The previous administration had to borrow and shift money around to continue normal city operations. That had a 29 million dollar hole in our general fund."
The special census does not cover the entire city. Instead, it targets just under 4,000 households across Aurora's ten wards.
Rather than focusing on areas with the lowest participation rates in the 2020 census, officials said they chose to concentrate on newer construction neighborhoods where they believe the effort will be most successful.
Laesch said concerns about participation remain in some communities.
"In Hispanic neighborhoods there has been a heavy presence of ICE in the City of Aurora. Some of those people don't feel safe being recounted," he said.
City officials emphasized that the Census Bureau data is not shared with federal law enforcement agencies.
"It's safe. It's confidential. There is no citizenship question on this at all. All those fears people have. We want to ease those," Cameron said.
Residents in the designated areas have until Aug. 24 to submit their responses online. After that date, federal census workers will go door-to-door in an effort to ensure maximum participation.
To see which homes are included in the special census, visit yourvoice.aurora.il.us