What could cause swollen lymph nodes in my groin?

Many: Most common cause is a nearby infection or irritation causing the lymph nodes to enlarge, such as bladder or urinary problems. Sometimes skin irritation or leg injury or wound can also cause enlarged groin lymph nodes. Less common is lymphoma. Would need to see your doctor if the lymph nodes persist and do not resolve.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.