Philadelphia and local governments across the country have been preparing for a year or more for the 2020 Census, the country’s largest peacetime mobilization and the population count that will shape national policy and funding for the next decade. And now it’s finally here.

Starting Thursday, residents nationwide will receive invitations from the Census Bureau to answer the census. Roughly 143 million households will get the mailing between March 12 and March 20.

Here’s what you need to know:

The point of the decennial census

The U.S. Constitution mandates a population count every 10 years. This count determines the allocation of hundreds of billions of dollars to state and local governments, the share of seats each state has in the U.S. House, and the boundaries of voting districts.

At stake is federal funding over the next decade for housing assistance, schools, highways, medical centers, and community development. Businesses use population data to decide where to open. Nonprofits and local governments use it to focus resources. Other agencies use census statistics for their own analyses.

Census time line

March 12-20: The majority of households will receive invitations in their mailboxes to respond to the census online.

March 16-24: Households will receive a reminder letter.

March 26-April 3: Households that haven’t responded will receive a reminder postcard.

April 8-16: Households that haven’t responded will get a reminder letter and a paper questionnaire.

April 20-27: Households will get a final reminder postcard.

May-July: Census takers visit households that have not yet answered their questionnaires online, by phone, or by mail.

Dec. 31: Deadline for President Donald Trump and Congress to receive apportionment counts.

March 31, 2021: Deadline for the Census Bureau to send data to states so they can redraw legislative districts based on population shifts.

Questions on the 2020 Census

The main purpose of the census is to count people, so the form asks how many people live in the household, with a reminder to count babies and nonrelatives. Questionnaires also ask households for demographic information, including the sex, names, dates of birth, and races of people living in a home, whether occupants own or rent, and a phone number census workers can call to follow up if necessary.

The form is nine questions for the first person and seven or fewer for each additional household resident. The decennial census does not include inquiries about housing characteristics or income. The Census Bureau does not ask for Social Security numbers, bank information, or money.

» READ MORE: Participate in the 2020 Census? Most adults say they will, but others aren't convinced

Language help for non-English speakers

Residents can respond to the 2020 Census in more languages than ever before.

Paper questionnaires are available in English and in Spanish. Census invitations will include an insert in 12 languages inviting online and phone responses in those languages. Residents can call for help with their forms in these languages: English, Spanish, Mandarin and Cantonese Chinese, Vietnamese, Korean, Russian, Arabic, Tagalog, Polish, French, Haitian Creole, Portuguese, and Japanese. Additional guides in 59 non-English languages, braille, and large print also are available.

Some challenges to a complete population count

The 2020 Census is the first decennial census for which the federal government is encouraging households nationwide to answer questionnaires online, which saves the Census Bureau time and money. But community activists are concerned the digital divide may depress population counts.

Libraries throughout Philadelphia and nationwide will host residents who want to use their public computers and internet access to fill out forms. Philadelphia plans to host events at which residents can fill out the census on wireless devices. Any resident also can answer the census by phone or mail.

» READ MORE: Possible positive coronavirus side effect? More people may fill out the 2020 Census online

Census officials and community leaders also are fighting against misinformation and confusion. Some residents throughout Southeastern Pennsylvania received forms from the Republican National Committee in February titled “2020 Congressional District Census,” which local government officials feared would lead residents to mistakenly believe they had already filled out the census when the Census Bureau asks for responses starting this month.

» READ MORE: 2020 Census concerns in Camden — where ‘thousands’ avoided 2010 count — reflect worries nationwide

In general, fewer people trust the government now than they did in previous census counts, which can make persuading people to share personal information difficult. The bureau and local officials are trying to combat that mistrust by emphasizing that, by law, the bureau cannot share residents’ personal information with anyone, including other government agencies.

In an ongoing challenge, each census misses some people. Historically undercounted communities include young children whom caregivers might not think to count and immigrants and racial minorities who don’t trust the government. The Census Bureau and state and local governments have been focusing on reaching these communities.

And even though a citizenship question will not appear on census questionnaires, bureau and community officials worry immigrant communities will be less likely to respond to the census out of fear built up during more than a year of debate over the question.

State and local governments and immigrant and community groups sued the Trump administration to stop it from adding a citizenship question to the census. The government dropped its pursuit of the question after the U.S. Supreme Court temporarily blocked it.

» READ MORE: Timeline to the Supreme Court's ruling on the citizenship question on the 2020 Census

Census Bureau officials also were worried the country’s low unemployment rate would make recruiting census takers more difficult. But Philadelphia is well ahead of its recruitment goal, and nationwide, more than 2.6 million people have applied for positions. The bureau is aiming for 2.7 million.

The people who will go door-to-door

The Census Bureau has started hiring the part-time, temporary workers who go door-to-door collecting responses from households that have not answered their questionnaires. The bureau is accepting applications for census takers through the end of May. It is hiring up to 500,000 workers.

Workers must have Social Security numbers, be at least 18, pass background checks, and complete training. They will wear ID badges with their photo, a U.S. Department of Commerce watermark, and an expiration date. For those worried about the coronavirus, the Census Bureau emphasizes there is no need for physical contact with workers and encourages online responses.

The bureau hiked hourly pay for census takers in January to boost lagging recruitment and has boosted pay again in some counties. Philadelphians can earn $25.50 an hour. Hourly rates in the rest of the region range from about $20 in Delaware, Burlington, Camden, and Gloucester Counties to $27.50 in Chester County.

In March and April, census takers will count people who are homeless and people living in group housing, such as college students and residents of senior centers.

» READ MORE: 2020 Census 'listers' walked through the country's neighborhoods to verify millions of addresses

Preparing for the 2020 Census

On the advice of the Census Bureau, state and local governments formed “complete count committees" to spread awareness about the census, encourage residents to participate, and target communities that historically have been undercounted.

Philadelphia and other cities across the country began preparations in 2018. Philly started planning nine months earlier for the 2020 Census than it did for 2010. It has trained thousands of people to be Census Champions, those equipped to teach members of their communities about the census. The director of the Census Bureau called Philadelphia’s Census Champions program a national model.

Philly Counts 2020, the city’s effort to make sure residents are counted, and similar groups across the region have hosted census job fairs and awareness events. They plan to continue their efforts through July.

» READ MORE: Philadelphia trains more than 2,000 people in 1 day to be 2020 'Census Champions'

State funding for the census has varied widely. California, for example, has devoted more than $100 million — more than $2.50 per person — for census work. New Jersey’s budget includes $9 million for census efforts — roughly $1 for every resident.

Pennsylvania’s census commission asked for the same allotment per resident — nearly $13 million in total — but the state’s budget did not include census funding. Gov. Tom Wolf later authorized the State Department to use up to $4 million from the general fund.

The Census Bureau is spending $500 million on advertising alone. It’s the “most robust” ad campaign in census history, officials said.