There are a few elements to the answer to this question.
If you were married before, divorced and are not currently married, then you can approach the Church for initiation. However, the Church will consider you to be married even though the law does not consider you to be.  That is because the Church views marriage as a permanent state of life until a partner dies.  As long as you do not re-marry, that does not prohibit becoming a Catholic.  If you wish to re-marry, read on!
If you were married once before, are divorced and re-married the answer is a bit less cut and dry. Because the Church considers marriage a permanent state of life, it is not easy to dissolve a marriage in the Church.  The process that may be able to say that your marriage was not begun with the intention for it to be permanent is called an annulment.  If this is your situation, it’s best to talk with the pastor or the RCIA Director to get some sense of how this might work for you.
If you were married and your spouse has died, you are free to approach the Church for initiation.