According to the USDA Frankfort is in USDA Zone 5b. Here is some general info for USDA Zone 5b to help you get started.
| Average Date of Last Frost (spring) | April 15 |
| Average Date of First Frost (fall) | October 15 |
| Lowest Expected Low | -15°F |
| Highest Expected Low | -10°F |
This means that on a really cold year, the coldest it will get is -15°F. On most years you should be prepared to experience lows near -10°F.
You can view the USDA Zone map for Illinois here:
Below is a list of planting guides for Frankfort, IL. These guides are based on data from Zone 5b.
Vegetables
Herbs
Flowers