Garcetti joined San Jose Mayor Sam Liccardo to spread the message because there's a lot at stake, he says.
"Everybody counts, and we have just three weeks to complete a full and accurate tally of every person in our cities and nation,'' Garcetti said. "What's at stake is nothing less than fair representation in Washington, D.C. and billions of dollars of investments in the health, welfare and safety of our communities."
According to the mayor's office, many large cities currently have response rates under 60%, which is well below the 66.5% national response rate in the 2010 Census.
Here's what you need to know about the 2020 Census
The Census is mandated by the U.S. Constitution to take place every 10 years. Census data is used to help determine how many representatives are sent to Congress from each state over the next decade and how much federal funding will return to local governments.
As the largest city in the hardest-to-count county in the nation, there are billions of dollars on the line with the Los Angeles Census response, Garcetti said.
The deadline for completing the census has changed a few times but the United States Census Bureau says it now plans to finish collecting data by Sept. 30.
Click here to fill out the 2020 Census.
How your community can lose money when you don't fill out the census
City News Service contributed to this report.