Polycrystalline diamond compact (PDC) cutting elements include leached and un-leached regions. The leached region may be or include a leached annular region. An inner boundary of the leached annular region remote from a side surface of the polycrystalline diamond may have a non-linear profile in a plane extending through the PDC cutting element along a longitudinal axis of the cutting element. Methods of forming PDC cutting elements include configuring polycrystalline diamond of a PDC cutting element to have such a leached annular region with a non-linear profile. Earth-boring tools may be formed that include such PDC cutting elements.