I was out sick and missed the last 1/4 of the school year. I absolutely bombed the final and ended with a C+ in honors chemistry. I still have a high gpa with a 3.75 and have a 1550/1600 on the sat, with a 750 on verbal and an 800 on math. I’m applying mostly to large flagship state institutions like UIUC, UW Madison, Umich, etc.
Be sure to have your guidance counselor address the illness and missed school time in the LOR. One poor grade shouldn’t sink the ship.
UIUC admits students with far less SAT scores and lower GPAs than that, as of the latest academic year, but past admittance statistics is no guarantee. But for that school at any rate (I can’t speak to the rest) a simple letter would more than suffice. You could perhaps even tackle the situation as a potential essay (I haven’t looked at the questions yet but my son will be applying there. He got a C in honors English sophomore year that I honestly never even thought about trying to explain.) A single grade anomaly like that on an otherwise stellar academic record shouldn’t be a problem there. Of course I am no admissions expert but my son has friends who are in the latest two cohorts of freshman and I know their stats aren’t what yours are.