Next time try PLANTS, not sets. There are a lot of factors that go into onions, not the least of which is the quality of your soil. Peruse the attached publication. It is from 1994, but the general principles are the same. Check with your extension service for the varieties that do well in your area.
hortster

Here is a link that might be useful: Publication on onions

Concur. Few people can grow large onions from sets. They are mostly used for green onions. They also require a heavy dose of nitrogen and they are heavy feeders. They are a leaf vegetable not a root or tuber.As hortster stated variety is important so pick one for your growing conditions.

I, too, concur. For years we grew onions from sets and were never really satisfied with size. A few years I really put the nitrogen to them and that helped, but we still didn't get what we really wanted.

Three seasons ago I made the switch to plants but maintained some sets as a control. The results were dramatic. The plants producted much larger onions.

The other thing about plants is that you are able to purchase the type that do best in your area. Bulbing is affected by the length of your days and onions are sold for short, intermediate, and long days. It appears that you should be using an intermediate day onion. For more information, you might want to consult the following site.

Here is a link that might be useful: onion types

Thank you all so much for the great information! I will use plants next year. Do you start from seed or buy the bundled plants?
I fed these quite a bit, but probably not as much as they required. I will keep that in mind as well.
Thanks again!!