I started receiving state disability in October and went back to work in July. Do I file for the disability I received from January to July?

Not sure of your state regulations but is filed as income on Federal return. State should give you a 1099 or similar form.

It depends on the nature of the disability payments.

If the disability payments were provided by your employer, then they ARE taxable.

However, if you purchased the disability insurance yourself with after-tax money, then the disability is tax-exempt.