Founded in 1838, Mercer County is one of 21 counties in the state of New Jersey. Historically, Mercer County was formed from Burlington County, Hunterdon County, Middlesex County, and Somerset County. The city of Trenton is the county seat. With FIPS code of 21, Mercer County has a population of 385,898 and area of 226 square miles (585 km2).
List of all cities in Mercer County, NJ alphabetically
| City/Town | Postal Code | Area Code |
| Division of Revenue, NJ | 08646 | 609 |
| 08695 | 609 | |
| East Windsor, NJ | 08520 | 609 |
| Educational Testing Service, NJ | 08541 | 609 |
| Ewing, NJ | 08560 | 609 |
| 08618 | 609 | |
| 08628 | 609 | |
| 08638 | 609 | |
| Ewing Township, NJ | 08618 | 609 |
| 08628 | 609 | |
| 08638 | 609 | |
| Groveville, NJ | 08620 | 609 |
| Hamilton, NJ | 08609 | 609 |
| 08610 | 609 | |
| 08611 | 609 | |
| 08619 | 609 | |
| 08620 | 609 | |
| 08629 | 609 | |
| 08650 | 609 | |
| 08690 | 609 | |
| 08691 | 609 | |
| Hamilton Square, NJ | 08690 | 609 |
| Hightstown, NJ | 08520 | 609 |
| Hopewell, NJ | 08525 | 609 |
| Lawrence, NJ | 08648 | 609 |
| Lawrenceville, NJ | 08648 | 609 |
| Mercerville, NJ | 08619 | 609 |
| Nj Income Tax, NJ | 08647 | 609 |
| North J Income Tax, NJ | 08647 | 609 |
| North J State Income Tax, NJ | 08645 | 609 |
| Pennington, NJ | 08534 | 609 |
| Princeton, NJ | 08540 | 609 |
| 08541 | 609 | |
| 08542 | 609 | |
| 08543 | 609 | |
| 08544 | 609 | |
| Princeton Junction, NJ | 08550 | 609 |
| Princeton Township, NJ | 08540 | 609 |
| Princeton University, NJ | 08544 | 609 |
| Robbinsville, NJ | 08691 | 609 |
| State Income Tax, NJ | 08645 | 609 |
| State of Nj Motor Vehicles, NJ | 08666 | 609 |
| State of Nj Taxation Dept, NJ | 08646 | 609 |
| 08695 | 609 | |
| Titusville, NJ | 08560 | 609 |
| Trenton, NJ | 08601 | 609 |
| 08602 | 609 | |
| 08603 | 609 | |
| 08604 | 609 | |
| 08605 | 609 | |
| 08606 | 609 | |
| 08607 | 609 | |
| 08608 | 609 | |
| 08609 | 609 | |
| 08610 | 609 | |
| 08611 | 609 | |
| 08618 | 609 | |
| 08619 | 609 | |
| 08620 | 609 | |
| 08625 | 609 | |
| 08628 | 609 | |
| 08629 | 609 | |
| 08638 | 609 | |
| 08645 | 609 | |
| 08646 | 609 | |
| 08647 | 609 | |
| 08648 | 609 | |
| 08650 | 609 | |
| 08666 | 609 | |
| 08690 | 609 | |
| 08691 | 609 | |
| 08695 | 609 | |
| Uppr Free Township, NJ | 08691 | 609 |
| West Trenton, NJ | 08628 | 609 |
| West Win Tow, NJ | 08550 | 609 |
| West Windsor, NJ | 08550 | 609 |
| Windsor, NJ | 08561 | 609 |
| Yardville, NJ | 08620 | 609 |