Sexually transmitted infections (STIs), often referred to as STDs, impact millions of people around the United States and thousands of people here in Illinois. Rates of several infections have risen in our state in recent years, and for some of the most common conditions, infection rates in Illinois outpace the national rates.

According to federal data, more than 2 million cases of chlamydia, gonorrhea, and primary and secondary syphilis were reported in the U.S. in 2017, marking the fourth consecutive year in which rates of these STIs rose sharply across the country.

What STDs and STIs are most common Illinois, which rates are on the rise and by how much, and which areas of Illinois account for the highest rates of certain diseases and infections? Let’s explore available data published by public health groups like the federal Centers for Disease Control and Prevention and the Illinois Department of Public Health.

Chlamydia Rates in Illinois

About 75,000 new cases of chlamydia were reported in Illinois in 2017, for a population-adjusted rate of 589.9. This puts Illinois among the 10 states with the highest rate of new chlamydia cases that year.

Chlamydia infections per 100,000 population

10 highest
1. Alaska 799.8
2. Louisiana 742.4
3. Mississippi 707.6
4. New Mexico 651.6
5. South Carolina 649.8
6. Georgia 631.4
7. North Carolina 619.7
8. Alabama 615.5
9. New York 591.6
10. Illinois 589.9
10 lowest
41. Massachusetts 430.4
42. Minnesota 426.4
43. New Jersey 394
44. Idaho 368.4
45. Wyoming 365.8
46. Maine 342.1
47. Utah 332.2
48.New Hampshire 330.5
49. Vermont 297.5
50. West Virginia 226.1

Illinois’ chlamydia infection rate in 2017 was the highest of any state in the Midwest, and the closest neighboring state was Missouri, which came in 19th. The state’s chlamydia infection rate rose 5% between 2016 and 2017 and has surged by 20% since 2013. Some good news, though: Illinois’ chlamydia increase since 2013 is among the lower half of increases across the country. Infection rates in Connecticut rose by an incredible 43% in the same time period.

Gonorrhea Rates in Illinois

More than 22,000 new cases of gonorrhea were reported in Illinois in 2017. That makes the state’s population-adjusted rate 186.4 per 100,000 people, placing the state 17th in the country.

Gonorrhea infections per 100,000 population, Midwest

1. Missouri 214.8
2. Ohio 206.4
3. Illinois 186.4
4. Indiana 178.4
5. Michigan 158.6
6. Kansas 156.3
7. South Dakota 149.1
8. Nebraska 139.1
9. Wisconsin 132.6
10. North Dakota 127.4
11. Iowa 119.9
12. Minnesota 118.1

 While Illinois comes in just 17th in the whole country, it’s ranked third-highest among other Midwestern states and comes in behind only one neighboring state, Missouri. While the state has seen a 13% increase in the rate of gonorrhea infections, that increase is among the lowest in the country. Vermont saw its gonorrhea infection rate jump 62% between 2016 and 2017 alone.

New gonorrhea infections per 100,000 population by year, Illinois

2013 2014 2015 2016 2017
127.8 124 133.2 164.8 186.4

All states have seen their gonorrhea rates rise since 2013, but Illinois’ 46% increase, while cause for concern, is actually one of the smallest increases in the country. Gonorrhea infections rose the most in Wyoming, where the rate increase by more than 500%.

Syphilis Rates in Illinois

Just over 1,000 people in Illinois were diagnosed with primary or secondary syphilis in 2017. The CDC also reports cases of congenital syphilis, which is passed from mother to baby, but we’ve omitted those cases for this report. Syphilis is relatively rare among STDs, but it’s one of the most potentially dangerous, and untreated syphilis can even be fatal.

Illinois’ 1,225 total new cases of syphilis in 2017 made the state’s population-adjusted rate 9.6 per 100,000 population, putting the state in the top 10 highest states.

New primary and secondary syphilis infections per 100,000 population

10 highest
1. Nevada 20
2. California 17.1
3. Louisiana 14.5
4. Georgia 14.4
5. Arizona 13.6
6. New York 11.9
7. Florida 11.6
8. North Carolina 11.2
9. Mississippi 10.4
10. Illinois 9.6
10 lowest
41. Idaho 3.8
42. West Virginia 3.4
43. Iowa 3.2
44. New Hampshire 3.2
45. Connecticut 3.1
46. Wisconsin 3
47. Nebraska 2.3
48. Vermont 2.1
49. Alaska 1.8
50. Wyoming 0.7

Illinois’ syphilis infection rate is the highest among the state’s neighbors, with Missouri’s rate 8.3 per 100,000 just over a point behind Illinois. In a bit of good news, the state has seen a slight drop in the primary/secondary syphilis rate. The rate in 2016 was 9.8 per 100,000, so it fell about 2% between 2016 and 2017. Don’t celebrate too much, though, as a longer timeline shows a 55% increase since 2013.

New syphilis infections per 100,000 population by year, Illinois

2013 2014 2015 2016 2017
6.2 6.7 8.4 9.8 9.6

Since 2013, just four states have seen their syphilis rates fall (Alaska, South Dakota, Iowa and Michigan), and Montana and Maine have seen insane jumps of 820% and 513%, respectively.

HIV & Other STD Rates in Illinois


About 1,200 people in Illinois were newly diagnosed with HIV in 2017 for a rate of 11.7 per 100,000 people, enough to place the state in the top 20 among states with the highest new infection rates. See HIV test options.

On the bright side, though, the 2017 rate was lower than the rate for 2016, with the state marking about a 17% decline in the HIV infection rate.

Hepatitis B

Nearly 40 people in Illinois were diagnosed with acute hepatitis B in 2016 (the most recently available data, which makes for a huge decrease in the prevalence of the virus in Illinois. The state’s rate of infections has fallen more than 130% since 2012. See hepatitis test options.


By far the most common sexually transmitted infection, most sexually active people will contract human papillomavirus at some point in their lives. In fact, the disease is so common, there isn’t solid data in Illinois on how many people have it or are diagnosed every year, but the CDC has reported an HPV-related cancer rate of about 12.22 per 100,000 people for our state. See HPV test options.

STD Rates in Chicago & Other Illinois Cities

Chicago is the country’s third-largest city and accounts for nearly 1 in 5 residents of Illinois. That could help explain why the city serves to dramatically skew the state’s STD figures. In fact, for all three of the CDC-monitored STDs (chlamydia, gonorrhea and syphilis), Chicago’s rates outpaced the state as a whole in 2016.


Chicago rate: 1,104.6 per 100,000

Illinois rate: 562.7 per 100,000

Chicago accounted for 41.2% of the cases in the whole state.

Top 10 counties (infections per 100,000 population, 2016)

1. Jackson 1,094.40
2. Peoria 851
3. Pope 850.1
4. Cook 790.3
5. St. Clair 765.4
6. McDonough 732.9
7. Macon 710.5
8. Champaign 707.7
9. Vermilion 660.3
10. Sangamon 658.9


Chicago rate: 402 per 100,000

Illinois rate: 165.2 per 100,000

Chicago accounted for 51.1% of all cases.

Top 10 counties (infections per 100,000 population, 2016)

1. Peoria 323.3
2. Macon 319.6
3. St. Clair 301.8
4. Pulaski 292.2
5. Sangamon 262.8
6. Cook 262
7. Alexander 254.9
8. Winnebago 240.8
9. Vermilion 236.4
10. Jackson 186

 Primary & secondary syphilis

Chicago rate: 30.2 per 100,000

Illinois rate: 9.8 per 100,000

Chicago accounted for 64.5% of syphilis cases.

Top 10 counties (infections per 100,000 population, 2016)

1. Cook 19.6
2. St. Clair 7.8
3. Greene 7.2
4. Will 6.8
5. Logan 6.6
6. McDonough 6.1
7. Wayne 6
8. Bureau 5.7
9. Peoria 5.4
10. Sangamon 5.1


STDs are incredibly common, with virtually all sexually active people coming down with at least one of them at some point in their lives. And while a few can have devastating, even deadly consequences, most of them are treatable and largely preventable. The key is knowing your status so that you can seek treatment and avoid passing your disease to your sexual partners.

Additional References

Note: The CDC publishes comprehensive STD data on only three of the many conditions that are sexually transmitted — chlamydia, gonorrhea, and primary and secondary syphilis. Many other STDs are not classified as nationally notifiable diseases, meaning states are not legally obligated to report infection rates. Also, while the CDC collects data for the District of Columbia, the population density of the district prevents it from being included in rankings.


by AtHomeSTDKit

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