It is usually celebrated a day before Ganesh Chaturthi. Wikipedia states below
This festival celebrates the goddess Gowri or Gauri, (also known as Parvati) who is venerated as the mother of Lord Ganesh. It is usually observed by married women and is a significant festival in Karnataka.1 It is known as Hartalika in the North Indian states of Uttar Pradesh, Bihar, Jharkhand, Rajasthan, Chhattisgarh, Maharashtra and Madhya Pradesh.
What I have heard from my grandfather is that this is the day Gauri (Goddess Parvati) created Ganesh to guard her while she bathed. Story goes Lord Shiva unaware of this boy beheads and them attaches with Elephant head. Hence the next day Ganesh Chaturthi. Here I am adding the link to the story I just narrated above.
Is this day celebrated in other states? If so what is the significance.