Johnson County, Illinois · Vienna
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With 14% of homes built before 1960 and about 19 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
March brings the most downpours to Johnson County, part of 13.7 heavy-rain days a year. Check the sump first.
Sewage backups in Johnson County spike on heavy-rain days, about 13.7 a year, when sewer mains fill up and water finds the lowest drain.
Johnson County's wettest day in the 2015–2024 record brought 3.12 inches, and about 64 freeze-thaw days a year mean ice dams in some winters.
23% of occupied homes in Johnson County heat mainly with wood or propane, above the Illinois county median of 16.5%.
About 79 nights a year here stay at 65°F or warmer, so basements and crawl spaces can grow mold even without a leak.
Local risk profile
Johnson County covers 344 square miles of southern Illinois, with about 13,376 residents and 5,541 homes. Besides Vienna, the county seat, the biggest communities are Goreville, Buncombe and Cypress. Much of its housing is recent, with a median build year of 1985.
41/100 Water Damage Risk Index: Moderate Johnson County ranks 84 of 102 Illinois counties. See the statewide ranking and method.The three factors where Johnson County ranks highest compared with other Illinois counties.
Johnson County is milder than most of Illinois, but not mild enough to skip winterizing. It averaged 75 freezing nights a year over 2015–2024, 19 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 102 Illinois counties that's 95th.
Cold snaps are the real risk. The worst in the record lasted 11 days below freezing (ending February 2021), and the low bottomed out near -8°F on February 19, 2015.
The freeze season here runs December to February, with January the coldest. If you travel then, leave the thermostat at 55°F or above and open sink cabinets on outside walls.
On average the first fall freeze arrives around Nov 1 and the last spring freeze around Mar 28.
Heavy rain is a bigger factor here than in most of Illinois. Of roughly 51 inches of yearly precipitation, the damage comes from the 13.7 days a year with an inch or more, ranked 2nd of 102. March, April and July see the most. The single wettest day in the record: 3.12 inches, November 1, 2018. Multi-day storms matter most for basements; the wettest three days on record here totaled 5.17 inches (through September 29, 2024).
The temperature crosses 32°F in both directions on roughly 64 days a year. Each cycle melts and refreezes water at roof edges and in foundation cracks, which is how ice dams and basement seepage get started.
Housing
44% of homes in Johnson County predate 1980, below the Illinois county median of 65.9%, which ranks 96th of Illinois's 102 counties.
29% of homes were built in 2000 or later, more than in most of Illinois. Newer plumbing rarely corrodes, so damage here tends to come from appliance supply lines, water heaters, sump pumps and storms.
The 1980s and 1990s account for 28% of the county's homes. If yours is from those decades, look under the sinks and at the water heater for gray plastic pipe stamped PB, which is polybutylene and leak-prone.
27% of homes are manufactured or mobile homes, above the Illinois county median of 5.6%. Their water lines run under the floor behind the skirting, so a torn skirt or failed heat tape freezes them faster than lines in a site-built house.
With 26% of homes empty at survey time, landlords and seasonal owners should shut off the main or schedule checks in winter. An unheated vacant house is also where many policies limit freeze coverage.
Beyond water
Summer nights that don't drop below 65°F, a good marker of humid air, come about 79 times a year here, above the Illinois county median of 51. Mold grows when indoor humidity stays above about 60%, the EPA's ceiling. A basement dehumidifier set to 50% and drying anything wet within 24 to 48 hours prevents most problems.
Mold remediation: what to expectBy main heating fuel, Johnson County homes break down as 16% utility gas, 61% electric, 21% propane and 2% wood. Propane heat is more common here than the state median. Have chimneys swept and fuel-burning appliances serviced each fall, and keep three feet clear around stoves and space heaters.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Johnson County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Williamson gets more pipe-freeze nights than Johnson. Pulaski County has the oldest housing nearby, with 62% of homes built before 1980.
By the numbers
| Factor | Johnson | Illinois median | Rank |
|---|---|---|---|
| Homes built before 1960 | 14% | 38% | 101 of 102 |
| Homes built before 1980 | 44% | 66% | 96 of 102 |
| Homes built 2000 or later | 29% | 15% | 6 of 102 |
| Manufactured or mobile homes | 27% | 5.6% | 1 of 102 |
| Vacant homes | 26% | 11% | 6 of 102 |
| Wood or propane heat | 23% | 17% | 25 of 102 |
| Nights at 20°F or colder | 19/yr | 35/yr | 95 of 102 |
| Days with 1 inch+ of rain | 14/yr | 8.4/yr | 2 of 102 |
| Freeze-thaw days | 64/yr | 81/yr | 97 of 102 |
| Muggy nights (65°F+) | 79/yr | 51/yr | 5 of 102 |
Rank 1 is the highest value. Bars run from the lowest to the highest Illinois county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Johnson County: freezing from December to February, heavy rain in March, April and July.
Sources: U.S. Census Bureau, ACS 2024 5-year estimates (2020-2024); weather from NOAA nClimGrid-Daily county averages (EpiNOAA), 2015–2024, averaged across the county; county boundaries from Census TIGER. Reviewed 2026-10-21. Methodology