You can google it, it's not some top secret information. Total numbers tracked over time aren't given each year so the last report was 2016 which gave the total as 60% of the illegal population was from visa over stays and since then reporting has indicated it's around a million people every year and studies have shown that once over stayed they don't often return home so it's not likely that 60% has changed.
So again, the clear choice is to tackle visa overstays if you're serious about decreasing the number of illegal immigrants in the country.