Figuring out when to visit a park that's open every single day of the year can be overwhelming. Most people consider the obvious, the crowd conditions, but fail to recognize other factors: Events held around Anaheim, the schedules of local school districts and even events occurring in the park itself.
It is widely assumed that summer is the busiest time at Disneyland, which is only partly true. Many estimates, including the Disneyland Linkage, place the weeks surrounding Christmas and New Years at the top of the list for most crowded.
New Year's Eve is infamous for the amount of people it attracts, and it is often reported that Disneyland simply begins refusing entrance to new guests. The maximum capacity for the park is around 85,000, and if you think of how small the walkways are in "normal" conditions, imagine it with 25, 30 thousand more people!
No matter how unbelievable it sounds, there are plenty of benefits to visiting Disneyland during the peak season. In spirit of the holidays, the park is given a complete makeover during the winter season, a main factor in drawing crowds. Even if you can't sneak onto Indiana Jones Adventure or the Matterhorn Bobsleds, it's worth a visit simply to witness the "snow" fall around Sleeping Beauty Castle and warm holiday tunes playing in the background.
You simply can't say the same for July and August, however. These months are also noted as some of the busiest, often ranking in at 55,000 visitors. Pair that with the beating California sun (average temperatures for the summer season range from 70-100 degrees Fahrenheit), and you've got both long lines and cranky guests surrounding you. It's also more common for groups to "cut" in front of you while waiting in summer's infamous lines: During my trip in early August, a group of around 20 managed to cut in front of my family while in the queue area for the Hollywood Tower of Terror.
Hour long waiting times and soaring temperatures are two things you have to be willing to accept if you visit in summer; they're both not going to change anytime soon. If you think past the rude people and sweat rolling down your face, you can have a pretty nice time. Just remember to ride some of the more popular rides, like Indiana Jones and Splash Mountain, in the wee hours of the morning and late at night. And don't even bother with Finding Nemo unless you've got a spare two hours on your hands.
You may be wondering about the so-called "off seasons" often mentioned with Disneyland fans. This phrase simply refers to the quieter, less crowded periods of time at the park, generally during the following: January, early and mid-February, September through October (excluding Columbus Day), November (also excluding the days around Thanksgiving, which are very busy), and the first two weeks of December.
In short: January, February, September, October and early December are best for visiting. March, April, June, July, August, November and late December are worst when it comes to crowds. May would probably be categorized in "worst" if anything, but most of the time it's sort of a neutral month.
Take this guide with a grain of salt as there are always exceptions, such as various school holidays, events taking place around the park and sudden changes in Disneyland's schedule. For the best trip possible, always make reservations months ahead of time and pay attention to what's going on in terms of events. And of course, consult the Disneyland Expert if you've got other burning questions!