My husband died on September 25, 2018. We have always filed jointly and we do not have any dependents living with us. What status do I file under on my 2018 return?

For tax year 2018 you will file as Married Filing Jointly since your spouse passed away in 2018.  For tax years 2019 and beyond if you do not re-marry and do not have any dependents then you will file as Single.