An inheritance and a gift from a third party intended as a gift to just one of you, are the two exceptions to the definition of marital property. However, as with pre-marital property, the increase in value of the inheritance of the gift during the marriage is marital property.
Also, all income generated from the non-marital property, is marital. So, assume you inherit an investment account with $100,000, but the market is good and the account increases in value to $125,000 and generates monthly interest income of $200. The initial inheritance of $100,000 is non-marital property, the $25,000 increase in value is marital and the monthly interest income of $200 marital and is used in calculating income for support purposes.
To be clear, it is only gifts from third parties clearly intended for one spouse that are non-marital. An example is a check or savings bond gifted in the name of just one of you.