The child custody dispute between Chicago parents Joseph Reyes and Rebecca Shapiro over the religious upbringing of their daughter provided a cautionary tale on what can go wrong with interfaith marriages, as discussed in a Washington Post article.
Child custody fights over religion may not always be as bitter as the Reyes-Shapiro dispute; but interfaith marriages, while on the rise, seem to be especially difficult to maintain. Data taken from the 2001 American Religious Identification Survey found that those who were in mixed-religion families were three times more likely to be divorced than those who were of the same faith (PDF).
A 1993 University of Illinois at Chicago study found that couples where both are members of mainstream Christian denominations have a one-in-five chance of divorcing; a Catholic and an evangelical Christian have a one-in-three chance; and a Christian and Jew who get married have greater than a 40 percent chance of getting divorced.
Countless other studies back this assertion as well, although clearer communication of intentions before getting married could go a long way.
Divorce attorneys in Chicago probably have a fairly clear perspective into this phenomenon and could even possibly suggest some methods for working out religious differences before ending the marriage. But as was illustrated by the Chicago custody dispute (Reyes, who is Catholic, wanted to expose his daughter to his religion over the objections of his Jewish ex-wife), these issues tend to play out in custody battles.
An Illinois family lawyer experienced in child custody matters should be able to help you work out an equitable plan for the religious upbringing of your child if your estranged spouse is of another faith.
FindLaw also provides information about how religion impacts child custody. Ideally, you want your child to feel loved no matter which religion they end up choosing once they're older.