my stepfather purchased a house while I was married and gifted it to me but his name is on the title and so is mine, is this marital property

Gifts and inhertiances are exempt from equal property division when getting a divorce in Wisconsin.  From the way you describe the transaction, you own the house jointly with your step father. Your share was received as a gift, so that portion, in my opinion, remains exempt from the marital estate. Now, if you and your husband are living in the home together,  have a mortgage on the property and pay it together, have done major repairs or renovations on the home, by doing some or all of those things, you may have changed the character of the property into marital, and your husband would have a claim to your 50% interest in the home. You don't offer enough facts to make that leap to determine if the property has been converted to marital by your respective actions pertaining to the home, during the marriage.