You raise a bunch of issues here, and don't give much information. The short answer is that you may want a post-nuptial agreement. If you want to know why, you can read the rest.
You say "my parent gave me money to buy a house . . . ." I'm assuming you didn't receive enough money to buy the house outright, but used the gift money as a down-payment and financed the rest of the purchase with a mortgage. Is that right?
You say your parents "gave" you this money. They didn't lend you this money. It would make a huge difference later on, in the event of a divorce. Assuming they gave it to you with no expectation of repayment, that would make it a gift and, therefore, the cash would be non-marital property. You can keep that gift (the cash) non-marital by not transferring it into some form of co-ownership with your husband. If you put it in a joint bank account, or buy a house and put his name on the deed, the transfer is assumed to be a gift to the marriage and the property becomes martial property. There are a few exceptions to this general rule, but you'll probably not qualify for one (at least not without a post-nuptial agreement).
If you put the house in your name only and keep your husband's name off of it, the house would (probably) be your non-marital property. If, however, you financed the purchase with a mortgage and you make those mortgage payments with marital property (all your marital paychecks), the house would probably "transmutate" (that's the word we use) into marital property by virtue of all that marital money pouring into it over the years..
California is a community property state. Illinois is not -- Illinois is a "common law" state when it comes to property division in divorce (see link, below).
Under Illinois law, assuming both you and your husband are on the deed, the IL house will be divided equitably (maybe 50/50, maybe some other ratio). As an aside, were the land in CA and both parties were on the deed,the property would be divided 50/50 -- whether you divorce in CA or IL. That's the distinction -- in Illinois, we divide property "according to equity" (and that's usually somewhere right around 50/50; in California, the property division is 50/50 . . . period. If a couple divorced in Illinois and owns property in California, the Illinois court is supposed to apply California law and divide THAT property 50/50 and the Illinois property "according to equity."
Solid answer by Wes Cowell.
Another issue to keep in mind with whether your parents "gave" or "lent" you the money would be whether or not a gift tax return was filed for the year in which the transfer from your parents occurred. If they intended it to be a gift, and the amount transferred from your parents to you exceeded the annual exclusion amount for the year in question, then your parents would have been required to file a gift tax return for that year, and pay gift tax on the amount transferred.
Also, consider whether the gift was intended to be a gift to you, or a gift to you and your husband. The facts and circumstances surrounding the gift will dictate this determination.
The foregoing is not intended to be specific legal advice, but rather general information. Because of the nature of this online, non-confidential forum, and because each and every family law case is different, it is impossible for any attorney to consider all of the facts of your specific case and provide a concrete answer. If you require specific legal advice, you should retain a qualified attorney in your area.
As stated by the other lawyers, there is not enough information to accurately answer your question. Some questions that need answers before a lawyer answers your question are: was the house purchased before or during your marriage, who signed the contract to purchase, in whose name was the house titled when it was purchased, were there sources of monies other than your parents for the down payment, was the title ever changed, who is obligated on the mortgage and has that ever changed?
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