Town Marshal is not a term used very frequently nowadays; however it is the same as police officer, or city officer. City officers do not answer to the county sheriff, they are separate jurisdictional bodies and each is responsible for their areas. They can have cooperative agreements, but they are not required to.
Wiki definition of marshal: In the American Old West, marshals, also called the "Town Marshal", were appointed or elected police officers of small communities, with similar powers and duties to that of a sheriff, while federal marshals would work in a larger, possibly overlapping area, especially in pioneering country. The word is still used in this sense, especially in the Southwest United States. (See List of Western lawmen). Still the name for some police forces.
Link provided below........
Hope this helps.