Half of the world's population will be online by 2018

Update, Nov. 25, 10:34 a.m. ET: Internet users will increase to 3 billion by the end of 2014, according to a new report from the United Nations International Telecommunication Union. The 4.3 billion people without online access live in developing countries, the report notes, so there are "important digital divides" that need to be addressed, despite the surge.

The Internet is about to get a little more crowded.

According to new data from market research firm eMarketer, the web will reach 2.89 billion users in 2015, or what equates to 42.4% of the world's population. This would mark a 6.2% jump from this year and reach about two in five people on a global scale.

The company projects even more growth in the upcoming four years; about 3.6 billion people (or half the world's population) will be online at least once a month by 2018.

This influx is largely due to the availability of lower-cost mobile phones and broadband connections in emerging markets, like India and Indonesia.

"Inexpensive mobile phones and mobile broadband connections are driving Internet access and usage in countries where fixed internet has been out of reach for consumers, whether that's due to lack of infrastructure or affordability," said Monica Peart, senior forecasting analyst at eMarketer.

"While highly developed markets are nearly saturated in terms of internet users, there's significant room for growth in emerging ones; for example, India and Indonesia will both see double-digit growth in each year between now and 2018. India and Indonesia will both see double-digit growth in each year between now and 2018."

Tech companies are doing a lot to get people online, too. For example, the nonprofit Internet.org is bringing free data to parts of Zambia in Southern Africa and plans to introduce the app to other parts of the world soon. Facebook founder and CEO Mark Zuckerberg launched the organization, along with support from other tech companies like Ericcson, Nokia, Qualcomm and Samsung.

eMarketer charted the countries where people of all ages access the Internet at least once a month; China tops that list with 620.7 million users in 2013, followed by the U.S. with 246 million.

However, the firm believes Brazil will jump ahead of Japan to No. 4 in 2014 and India will surpass the U.S. by 2016. The acceleration projection for China is noteworthy too and potentially make up three-quarters of a billion users in four years.