If your U.S. citizen partner has passed away, do not worry about being a permanent resident in the US through “adjustment of status,” without leaving the country. A widower of a US citizen can become a permanent resident and get a green card if he or she meets the eligibility criteria set by the USCIS.
For widower of a US Citizen who wants to get the US Green Card through adjustment of status.Source: U.S. Department of State
There are specific eligibility requirements for you to adjust status in the United States, and those don’t change even if your spouse is passed away. One of the major requirements for you is U.S. Citizenship and Immigration Services (USCIS) approve a petition categorizing you as the spouse of a U.S. citizen. Form I-130 or Form I-360 may be filed by your spouse. Yet, in all cases, you will need to prove that you were married to a US citizen and that you are a widow of deceased US citizen.Source: U.S. Department of State
If your spouse had filed an I-130, Petition for Alien Relative for you before his or her death, and it is still awaiting (awaiting a USCIS decision), then it is possible, in most cases, convert it to an I-360, Petition for Amerasian, Widow(er), or Special Immigrant upon learning of the spouse’s death. This petition is chosen by and for many types of people; in your case, it’s for a widow(er).
It is a must for you to let USCIS know about your spouse’s death by contacting with them handling the I-130 petition, along with a copy of the death certificate. No need to do anything else here. If the I-130 petition is eventually approved by USCIS, you have fulfilled the requirement of having an approved petition.
If USCIS approves the I-130 petition then it is clear that you are in the process of applying for adjustment of status when your spouse. USCIS will now proceed to process your adjustment of status application and you are not required to file another one.
If your deceased spouse did not file an I-130 petition for you before dying, you will be required to get an I-360 petition filed with and approved by USCIS. You must file the I-360 as soon as your partner dies but it should not be more than two years after the death of your partner.
You may file the I-360 petition before or at the same time as your adjustment of status application. it’s easier to file the I-360 and adjustment application simultaneously.Source: U.S. Department of State
As the widow or widower of a U.S. citizen, you apply for adjustment of status by preparing Form I-485, Application to Register Permanent Residence or Adjust Status,” as well as supporting forms and documents. The process is the same as it is for all other people who are applying for adjustment of status, with one important exception.
You or your children adjusting status with you do not need to submit Form I-864, Affidavit of Support. This is a form that is important and required by the person who petitioned for an immigrant, promising to support the immigrant financially. In your case, the USCIS is aware that you petitioned for yourself, and there is no need to prove that you can support yourself.Source: U.S. Department of State
The application filing fees to get Green card for widow(er) of US citizen is $435.Source: U.S. Department of State
If You are a “K-1” Fiance(e) Visa holder:
If you had a K-1 fiance(e) visa status when you have entered the U.S. You were supposed to marry your spouse within 90 days of coming to the United States. If you successfully did that, and later your spouse died, you can still adjust status.
If your fiance(e) had died before you were able to marry him or her, you are unable to adjust status, as you were never the legal spouse of a U.S. citizen. Similarly, if you stay in the U.S. and marry another person, you have no right to adjust your status based on that marital relationship. According to the rules, K-1 visa holders can’t adjust status as the spouse of anyone but the person who petitioned for the K-1 visa. Therefore, if you re-wed, you will have to leave the U.S. and get your immigrant visa through a U.S. consulate in your own country where you came from.Source: U.S. Department of State