Hi Griselda! Thanks for dropping by planDisney.
Currently, both a valid
admission ticket and
theme park reservation are required for entry to the parks at Disneyland Resort. So, while it is possible to purchase tickets in person, you can't enter the parks on days when there are no remaining theme park reservations. Popular days and parks can fill up and the availability of reservations is never guaranteed. For this reason, I recommend buying online. Even the night before gives you the confidence that you have both your ticket and reservation for a day of fun. Being turned away is an unmagical experience!
Of course, the earlier you make your reservation, the more availability you're likely to find. And if life gets in the way and you can't make your reservation, you have the option to modify it to another available date. If you've purchased a 1-day Ticket, which operates on the Tier system, you can choose any date of the same or lesser Tier. If you need to choose a new date in a higher Tier, you can call the
Tickets phone line, so a helpful Cast Member can assist you with the purchase. You'd simply have to pay the difference. Prices and terms are subject to change. But this gives you a lot of flexibility even after purchasing in advance.
You can always check theme park reservation availability with the handy
Theme Park Reservation Availability Calendar. Availability can change quickly. So don't count on a park being available if you do choose to show up and purchase the day of, as someone might have made that last remaining reservation right before you. My advice? Plan ahead: Purchase your tickets in advance and then modify them as needed.
I hope this helps!
Elizabeth