There were 350,000 cases reported in 2014 (which is the most recent data from the CDC) and most of those were in people under 25.
But because gonorrhea can present without symptoms, it's estimated that the actual number of cases each year is around 800,000. That's why it's so important to be tested regularly, regardless of how fine your genitals feel.
If left untreated, it can have serious health consequences. For women, that includes pelvic inflammatory disease, scar tissue, chronic pain, and infertility. In men, it can lead to inflammation of the tubes connected to the testicles, which can lead to infertility. It can also increase your risk of HIV infection.
Gonorrhea can be transmitted through vaginal, anal, or oral sex (it's passed through infected secretions or fluids). For that reason, condoms and dental dams are your best line of defense.