Just need an answer to my question. What is (block 15 of W-2) Ohio's Employer's State ID number?

[DanielV01]

It is just to the right of the OH.  It might be in a format like 52-xxxxxxx or something similar.

[Hal_Al]

If it's blank, and there's an amount in box 17, you will have to contact your employer to get that. Or you could try entering the federal EIN there. If boxes 16 & 17 are blank. you don't need the employer's state ID

[Hal_Al]

The Employer's State ID  for box 15 is OH (the postal abbreviation). It is not a number, The Employer's State ID  # goes in the un-numbered box between boxes 15 & 16.