Hello Perry,
Thank you for making a magical stop here at the Disney Parks Moms Panel. I hope you are having a Dapper Day!
Around the second to last week of September, Jack Skellington and his friends from Halloween Town will begin invading the 999 Happy Haunts from inside the Haunted Mansion and stay until the first week in January.
The Halloween overlay is expected to be completed before the last weekend in September. The Halloween festivities typically begin the last week of September and go through the end of October.
Halloween is a very popular time at the Disneyland Park with Mickey's Halloween Party throughout the month. You will want to keep checking the Disneyland website for details on Mickey's Halloween Party, as it is highly popular and is only held on select nights. The information on dates and times regarding Mickey's Halloween Party will usually be posted around mid July to early August, but this may vary and is subject to change.
I hope this helps and that you have a pixie-dusted time on your next visit. If you have any more questions, please visit us here and let us know how we can help you plan your magical vacation.
Wishing you Boo-tastic time!
~ Lynette