If you bought true sets. ( small dry storage onion bulblets) they will bulb if you are in the northern tier of states. Below the Mason Dixon line they don't bulb well and usually used as green onions (scalions) before they bolt.

I grew up in extreme NW Iowa (zone 4). Onion sets were all my parents ever used in the house garden. My mother got decent sized cooking onions that kept pretty well until late winter, once they were cured. I have gotten decent returns from Stuttgarter onion sets with very few bolts, myself, here in Minneapolis. Onion sets for replanting are specially grown to stay juvenile and so bulb up the next growing season (specifically from spring planting). Other types of small onions not stored properly, may be much more inclined to bolt, especially if they have been refrigerated for any length of time.

If makes some difference as farmerdill pointed out what your latitude or hardiness zone is. You can set that up in your profile and that helps others determine how to respond.