If I'm receiving SSI due to an illness as 66 do I still get social security check alsoand I still receive both SSI and social security
For the benefit of other readers, SSI is the abbreviation for Supplemental Security Income. SSI is a needs based program administered by the Social Security Administration, but the benefits aren't paid from the Social Security trust fund. Only people who are either blind, disabled, or age 65 or older can qualify for SSI payments.
SSI payments can supplement a person's other income, such as Social Security benefits, up to a certain level. The maximum individual federal SSI payment rate in 2020 is $783, but that amount would be offset by all but $20 of any Social Security benefits the person receives. So, if a person's only income is Social Security and SSI, the most they could be paid is $803. However, some states tack on state supplement payments to a person's SSI benefits in lieu of paying the state assistance amount separately.
To answer your question, though, if you're receiving both SSI and Social Security disability (SSDI) benefits, then your payment amounts likely won't change when you reach full retirement age (FRA). SSDI payments convert to regular Social Security benefits when a person reaches FRA, but that virtually never results in a change in the benefit rate.