Down Arrow Button Icon

This week, 12 more states are expanding COVID-19 vaccine eligibility to all adults. That means all adults are now vaccine-eligible in over half of the 50 U.S. states. That’s great news for many, and it reflects strong progress in the U.S. vaccination effort.

But officials and experts have warned to expect serious competition for appointments, especially in the early weeks of expanded eligibility. So if you haven’t yet navigated the lab-rat maze of portals to secure an appointment, it’s time to jump in before someone else gets your cheese (that is, vaccine).

Here’s what you need to know, starting with a broad overview of how the system works. A list of key vaccine signup resources in each state and D.C. follows.

This is a live list. To submit a resource for inclusion, please email david.morris@fortune.com.

The basics of U.S. vaccine signups

The most important thing to know about the U.S. COVID-19 vaccine signup system is that it doesn’t exist: There is no overarching national signup system. Instead, the Trump administration left it to individual states to figure out, so as you’ll see, some states have far more and better systems and tools than others. Many states provide only vaccine locators—maps or guides to vaccination locations such as hospitals. These generally don’t offer direct booking, so you’ll have to contact sites directly to book an appointment.

Only a handful of states and regions have built the pre-registration systems considered the ideal solution by many experts. These systems allow you to submit your information so you’ll be contacted when you are eligible or an appointment is available.

Meanwhile, there is a largely separate ecosystem of vaccinations offered through pharmacies, including chains and independent outlets. Fortune has put together this detailed guide to looking for pharmacy appointments.

Finally, to address the fragmentation of signups, nonprofits and other groups have built a variety of tools and resources for collating and distributing appointment information from various sources. These include Twitter bots with live appointment information. Where appropriate, we’ve included links to these local resources below.

But according to experts, the best resource may be local “Vaccine hunter” groups on Facebook, where residents of particular counties, cities, or small states share tips. There are perhaps thousands of these groups, so we’re only including some of the largest in our guide. To find the right one for you, use Facebook’s search feature and input something like “[your county] vaccine appointment group,” or check Vaccinehunter.org, a guide to these groups.

Before you sign up

Be ready to take any appointment you can access. That may mean booking one at an inconvenient time or a long distance away. There is incredible demand for appointments, and while things likely will get continually easier, you’re doing everyone a favor by taking the first slot you can make work, even if it’s less convenient than you might like.

Getting vaccinated is a selfless act. Vaccinations slow or stop the spread of COVID-19, and getting vaccinated doesn’t just protect you—it protects everyone around you. So as long as you’re not misrepresenting a health condition or otherwise cutting in line, grab that appointment and don’t hesitate.

The coronavirus vaccine is FREE to all U.S. residents. You should not be charged for the vaccine itself, or any administration fees.

Have your information handy. That includes a state I.D. and evidence of any medical condition impacting your eligibility (though enforcement of that documentation has been spotty). And while medical insurance isn’t required to get the vaccine without charge, you should have your account information ready if you do have insurance, both at signup and when you go to get vaccinated.

Nationwide resources

A handful of services will help you find vaccines across the country.

Pharmacy programs: Large chain pharmacies such as CVS and Rite Aid offer vaccinations. Our guide to pharmacy signup systems has more details.

Pharmacy vaccine locators: Vaccinefinder.org, Vaxxmax.com, Vaccinespotter.org, and Getmyvaccine.org all aggregate vaccine and appointment availability at pharmacies like CVS and Walgreens.

Tip: Most vaccine-search sites do not actually allow you to book appointments. One way to speed up your booking process is to open a pharmacy booking site, such as Walgreens’, alongside a search site, so you can book appointments as soon as you locate them.

Dr. B standby list: Because COVID vaccines have a limited shelf-life, leftover vaccines from missed appointments must sometimes be used on short notice before they go bad. This site helps connect you with unclaimed doses across the country.

Vaccinehunter.org: This is a spectacular catalog of state and regional Facebook groups that help members navigate the complexity of the appointment-search process. Vaccine-finding experts consistently recommend these groups as essential resources for finding a vaccine.

Vaccine signup resources by state

This alphabetical list includes government signup portals and waiting list pages, as well as unofficial regional vaccine-finding tools, from the most elaborate trackers to simple Twitter accounts. We will continue to update this list with new resources as we learn of them.

Tip: To quickly find your state on this list, type Control-F on a PC, or Command-F on a Mac, and search your state’s name.