Plastic is dumped into the ocean from every continent of the world. This plastic is not evenly disposed of. Certain countries dispose much more waste into the oceans than others. The majority of the plastic in the oceans within in recent year has come from multiple countries in Asia. The largest contributor to plastic disposal in the oceans is China by far. They mismanage nearly 8.80 million metric tons of plastic waste in a single year alone (2010). This statistic is only including plastic waste while much more other forms of waste are also dumped.

A total of 3.2 million metric tons of mismanaged plastic waste came from Indonesia and it is estimated that 1.29 million metric tons became plastic marine debris. The United States is also guilty of polluting oceans with plastic, but at a much lower level than China. Annually, 0.11 million metric tons of waterborne plastic garbage comes from the United States.
Niall McCarthy
https://www.statista.com/chart/12211/the-countries-polluting-the-oceans-the-most/N
Plastic has become such a necessity in every life that it is produced, used, and tossed, in every single human populated country on the earth. Many other countries beside China dump a massive amount of plastic into the oceans each year (but on a much smaller scale than China).

Source https://www.statista.com/chart/12211/the-countries-polluting-the-oceans-the-most/