Yes.
They are. Our entire workforce is less than a third of the population. Of filed tax returns, half pay roughly zero, or even negative tax.
You can get the raw data in the SOI (Statistics on Income) section of the IRS.gov website.
This chart summarizes:
Note that the lowest-earning half--50% of taxpayers--contribute very little, just 3.2% of federal income tax. The top 5% pay more than half.
This Snopes-type article (which I do not vouch for) claims Los Angeles has 10.2 million people, and 3.9 million workers:
It also makes a few points about the burden illegal aliens place on the healthcare system, e.g. half of births being to illegals (point #4).
Cheers, James Arthur