My father had early onset alzheimer's. What are my chances of getting it?

Depends. If you are already 61 and do not have it then it is unlikely you will get early onset dementia. See a specialist for more specific odds.
Is tissue available? If you have some of dad's tissues, it may be possible to check it for one of the known genetic causes, and determine whether you have it as well. Or you may be screened yourself without his information. Get with a clinical geneticist or someone else who's good at this sort of thing. Hoping for the best for you.