To make your lawn better you need to make your soil better because grasses need a good healthy soil to grow best in. Spreading something called "topsoil" around does little to help because "topsoil" can be anything scrapped off the top 4 to 6 inches of ground someplace. Start with these simple soil tests,
1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains� too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

which can aid in guiding you toward that good healthy soil.

Here is the 1-2-3 of lawn care as gleaned from these forums over the ages.

2. Water deeply and infrequently. Deeply means at least an hour in every zone, all at once. Infrequently means monthly during the cool months and no more than weekly during the hottest part of summer. If your grass looks dry before the month/week is up, water longer next time. Deep watering grows deep, drought resistant roots. Infrequent watering allows the top layer of soil to dry completely which kills off many shallow rooted weeds.

3. Mulch mow at the highest setting on your mower. Most grasses are the most dense when mowed tall. Bermuda, centipede, and bent grasses are the most dense when mowed at the lowest setting on your mower. Dense grass shades out weeds and uses less water when tall. Dense grass feeds the deep roots you're developing in 1 above.

4. Fertilize regularly. I fertilize 4 times per year using organic fertilizer. Which fertilizer you use is much less important than numbers 1 and 2 above.
   

But those won't help you get it going on the hillside. Which direction does the hillside face? Does it get much shade? Are people successful growing Kentucky bluegrass in your neighborhood?

The only problem with using more than 4x the amount on the Milorganite label is that it will smell. Corn gluten meal is absolutely not guaranteed to take care of anything except providing an excellent fertilizer experience. As a weed killer, you cannot rely on it.

The best tap-root pulling tool is the Weed Hound. Look it up. Everyone who has one swears by it (me too!). They have them at Home Depot.

Kentucky bluegrass will be the best lawn grass for the hillside. It forms a dense sod that will hold the soil in place. Turf type fescues are not as good at that. There are some pasture type fescues that are pretty good, but you probably don't want the weedy appearance. Just for motivation I'll add a photo of a Kentucky bluegrass lawn (flatland).

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William posted that photo here many years ago. He wanted to show off the improvement made simply by raising his mower height.

One problem with KBG is the seed takes 3 weeks to germinate. Many people give up the 3x per day watering regimen long before that and the results are unsatisfying. As you know, fall is the time to renovate. In the mean time you can treat your weeds as if they are the best weeds in the neighborhood. Follow the 1-2-3 above and it will look surprisingly good if not great. Some weeds will disappear from the good care and nothing else. Then when the summer heat breaks (might be July in WI), you can get going with the seeding project.

An article that I refer to that has been helpful to me is from Paul Wheaton at richsoil.com (I attached it below.) Here is an excerpt talking about the importance of soil depth that I think applies to your situation:

"My soil was only half an inch deep. Even weeds had a tough time growing. Below my half inch of soil was huge river rocks seperated by smaller rocks, sperated by sand. It bore no resemblance to soil. I added four inches of topsoil. This was done with two dumptruck loads at $100 a pop. It covered all of the weeds with enough soil that they could not work through - I could start from scratch with my grass seed of choice!

18 inches or more soil would be optimal. I have a friend that has soil this deep. While everyone else waters a dozen times or more over the summer, she waters just once or twice. She uses no fertilizer or pesticides. She has thick, dark green, weed-free grass which requires frequent mowing. Her lawn is about as "no-brainer lawn care" as you could get.

This is a good time to talk about soil quality too. There is a big difference between dirt and soil. Soil is rich in microbial life and has a lot of organic matter in it. Dirt comes in many forms and it's a challenge to get anything to grow in it. If you are getting "topsoil" delivered to your house, be prepared for it to bear more resemblance to "dirt". You may want to have compost also delivered to your house so that you can mix the two and have the beginnings for "soil". One part compost to two parts dirt is a good mix for lawn care."
Hope this helps!

Here is a link that might be useful: Organic Lawn Care for the Cheap and Lazy

While deep soil is certainly a benefit, you cannot just pile it on top of what you have. Someone reading this might, for a moment, believe they could pile up 18 inches of soil on top of their current soil. A split second later they should realize that is a ridiculous concept. I would propose that adding even 1 inch is a ridiculous concept unless you have low spots you are trying to fill. Piling up soil will result in dry soil and soil that flows across any surrounding concrete. It becomes a mess and always detracts from even a beautiful lawn.

If your soil is 1 inch deep and then rocks, you should drag out the rocks and start over. Growing grass on top of rubble is very frustrating. Growing grass in 1 inch of soil is similarly frustrating. If you want to lower the hassle factor of lawn care, you need a good base.

With this in mind, to the OP, you might delve a little deeper. Probe your hillside with a screwdriver looking for hard pan or rocks. It is a valid thought you might have overlooked. If you can stick (or pound) a screw driver 4-6 inches into the soil, you're okay. It may need to be softened, but that is doable. Certainly better than rocks.

If you can actually find good "topsoil" that might help although 18 inches worth is not necessary. "Topsoil" is defined as the top 4 to 6 inches of soil, so it can be anything the seller wants it to be and often is pretty useless stuff. Many peoples concept of "topsoil" is that it is loam, a specific soil type, which most "topsoil" is not.
Make your own topsoil by adding lots of organic matter to the soil you have.