I mailed my Federal tax returns. It's been 2 weeks since it has been delivered by USPS. However, I still can't find my refund status on the IRS website.

According to the IRS , it takes 4 weeks before the status of a paper tax return gets posted to the  Where’s My Refund? site.

Paper returns take significantly longer to process than e-filed returns. The status of your electronically filed tax return is posted twenty-four hours after received by the IRS.

See Tax Season Refund Frequently Asked Questions 

Thank you. That was helpful

Really helpful