We recently encountered a chimney that had been occupied by a raccoon for some time. We were unable to clean this chimney because of the chance that the raccoon had left droppings in this chimney. These droppings can contain a particularly unpleasant parasitic roundworm that can cause life-threatening symptoms if they are ingested ( See this CDC paper for more information: https://www.cdc.gov/parasites/baylisascaris/resources/raccoonlatrines.pdf)
Removing these droppings and sterilizing the infected areas requires specialized equipment and training which we do not have. In order to have them removed, you will likely spend a fair some of time and money, this can be prevented by having some sort of rain cap on your chimney. These can be ordered in a variety of sizes and styles from many websites, purchased from local hardware stores like Lowes or Home Depot, or, we can supply and install them for a fee.
Thanks for reading and have a great day.