Most of text in books and online articles refers to beginning of Jainism around 600 B.C. and founded by Lord Mahavir. Then there are some other references saying Lord Mahavir was 24th Thirthankar (God). Below mentioned are few such references available online.

877–777 BCE Parshva, 23rd Tirthankar of Jainism
599–527 BCE Mahavira, 24th and last Tirthankar of Jainism
599 BC. Jainism, Mahavira
Mahavira 599-527 BCE
877–777 BCE: Parshva, 23rd Tirthankar of Jainism.

and may more.

Now interesting point is that these reference do mention about 23th and 24th Thirthankar as founder of Religion but that surely can not be the case. First Thirthankar has to be the Founder of the religion. First Thirthankar of Jain is named Lord Rishabha. For the timeline of Lord Rishabha, there are varying timeline from 2000BC to 5000 BC. Other reference talks about time even earlier than that. But this should be accepted that Jainism did exist even before 600 B.C. Below mentioned are few more references to add more information about timeline.