One way to get lots of information about this is to join the School Counselor's facebook forum. I've noticed that it's different according to state, city, county, district, etc...
I live and work in Anne Arundel County, Maryland, and I work at the elementary K-5th grade level with a little over 450 students and just one counselor. It's not as terrible a ratio as some schools. We have an awesome school district, which is based on our county, and great support for school counselors. We are fortunate to have a general topic type "essential curriculum." We can vary from it and also be creative with our lessons. There are some lessons available that other counselor's have created and that the county specifically created for the "mandatory lessons." The mandatory lessons are related to Lauren's Law (substance abuse training for grades 3-5) and Erin's Law (child sexual abuse safety lessons). Depending on their student size and administration, school counselor's in our county typically teach lessons in each grade 2 times per month, but I must admit, I only go into 3rd-5th one time a month for lessons. The curriculum is dense and it's hard to ask for more. Fortunately, my lessons are all an hour long.
I work closely with my administrator (especially because I'm part of admin as we don't have an assistant principal), so I usually make a plan of lesson topics per grade and share it with her. She feels pretty confident in my skills and lesson topics, but I'm always flexible if we find we need some problem solving or friendship lessons based on things happening with student groups and grades at our school. Since we have a character trait for the month, I always incorporate one lesson for that for K -2 a month and do something short on it in the intermediate grades. I suppose some Principals have more involvement in your lesson topics and delivery, but I've been fortunate to have Principals that are supportive and give me the freedom to plan using the ASCA model standands and our county's essential curriculum outline.