Some states let you become a police officer with only a green card. Of these states, some require you to either declare your intent to become a citizen; to have filed citizenship paperwork; or to have become a U.S. citizen prior to being hired. Some police departments will let green card holders take the entrance exam, but will only hire them after they become U.S. citizens. Regardless of the state, you also must meet basic requirements to become a police officer.

Working with a Green Card

Rules governing someone's ability to become a police officer with only a green card vary by state and department. In Hawaii, for example, as long as you meet other basic employment requirements and have a green card, you can work for a police department. Most police departments in Colorado, including those in Colorado Springs, will hire you as long you have a green card and meet other basic employment requirements. The same holds true in Maine and in Illinois.

Meeting Citizenship Status Requirements

As long as you have a green card and have applied for U.S. citizenship, you can work for a police department in California. As long as you meet the other basic requirements, some states -- including Iowa and New York -- let you apply to become a police officer with just a green card, but also require you to become a U.S. citizen before your appointment. Some police departments, like the one in Anchorage, Alaska, will hire you if you have a green card as long as you've declared your intent to become a U.S. citizen. Applicants in the remaining states should contact state and local law enforcement authorities to find out the specific rules governing the citizenship requirements of police applicants.

How to Become a Citizen

If you have held a green card for at least five years and lived in the U.S. during this five-year period, you can apply for U.S. citizenship as long as you are 18 years old; reside in the U.S. 100 percent of the time between the date you apply for citizenship and the time of your naturalization; know how to read, write, and speak English; have an understanding of U.S. history and government; and have good moral character. Qualified spouses of U.S. citizens can apply for citizenship after living continuously in the U.S. for three years and meeting the other requirements.

Other Basic Requirements

Regardless of your citizenship status, you must meet some basic requirements to become a police officer. These typically include passing a written exam and a physical. Some requirements vary by state, such as how old you must be before applying to become a police officer or being hired as a police officer. For example, in New York City, you can apply to take the written entrance exam when you are 17-and-a-half years old but cannot be older than 35 years old. Indianapolis requires its police officers to be between 21 and 36 years old at the date of application. Some departments require its police officers to have some college education, while others require a bachelor's degree in criminal justice or a related field. Most departments require police officers to have a valid driver's license and pass a background check.