Put your cop hat back on. It suits us all much better.
Some jurisdictions have pre-trial programs for first offenders in similar cases, where the accused agrees to meet with a counselor or probation officer, without actually being convicted or being on probation. If all goes well after a few months the charges will be dropped.
However, the judge may not even mention this program. But a local lawyer will know how to get into it.
I gotta agree with this. At the very least, talk to a local defense attorney to learn what possible consequences are. Then you can decide whether it’s necessary to spend more money (probably a whole lot more) to hire an attorney to represent you in court. Perhaps you’d learn what several here have suggested, that it’s about equivalent to … let’s say jaywalking, and you can pay the fine and live your life. But maybe you’ll find out about some other potentially more dire consequences.
Don’t blow it off on your own assumptions that’s it’s nothing serious.
34 years experience says I do. It would be rare for 2 guys to be walking home from a party, one of them intoxicated (per the OP) and there not be odors of at least alcohol and highly likely smoke. Plus maybe some b.o. from being in a crowded house.
I’ve dealt with 2 guys “walking home from a party” hundreds of times. If they were at a party for even a moderate amount of time those odors are going to stick on them.
I agree with the advice to seek a free legal consultation. Nothing for the OP to lose doing that.
Pretrial diversion won’t be available for what sounds like a civil infraction. But then it won’t be necessary either.
If it’s free, great. If it’s not, pull out your wallet and pay.
Update:
I found out what the actual Illinois law is, as it pertains to this 19 year old.
Here’s a the important part…
Purchase, Possession, Receipt or Consumption of Alcohol by a Minor
Any person under age 21 convicted of the illegal purchase, possession, receipt or consumption of alcohol will have his/her driving privileges suspended for 6 months for a first conviction, 12 months for a second conviction and revocation of driving privileges for a subsequent conviction
He will be contacting an attorney to see if his village ordinance “citation” equals a “conviction” of the above in the eyes of the law. That’s what lawyers are for I guess.
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If he’s somewhere near a law school, he should give it a call. They often have students who will provide free research and even advice (under some important caveats) under the supervision of practicing lawyers and law professors. A couple of UW law students were extremely helpful to me in getting me out from foreclosure after a long bout of unemployment and being unable to pay my mortgage. I still have my home. 
Update:
The young man had his court date recently. He had a lawyer who talked to the judge and she reduced his citation to a “disorderly conduct” charge. Now he must pay a fine of $150 to the village plus $400 for his lawyer. So I guess things turned out O.K.
fwiw, He ended up using a lawyer that mailed out one of those un-solicited letters. I guess the lawyer was honest and upfront about his fees {$400 maximum} and has a lot of experience in these type of issues and “knew” the judge…
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Assuming disorderly conduct is a misdemeanor in his locality, this seems like a reasonable outcome.