Town Hall Address 1385 Rt. 22 Mountainside, NJ 07092 United States- Union County Website http://mountainside-nj.com/ County Clerk 908-232-2400 Ext. 237 1385 Rt. 22 Mountainside, NJ 07092 United States County Admin 908-232-2400 Ext. 239 1385 Rt. 22 Mountainside, NJ 07092 United States Assessor 908-232-2409 1385 Rt. 22 Mountainside, NJ 07092 United States Tax Collector 908-232-2400 Ext. 241 1385 Rt. 22 Mountainside, NJ 07092 United States Attorney 973-228-9900 1385 Rt. 22 Mountainside, NJ 07092 United States Mayor 908-232-2400 1385 Rt. 22 Mountainside, NJ 07092 United States Municipal Court 908-232-5335 1385 Rt. 22 Mountainside, NJ 07092 United States Town Hall Hours 8:30 am - 4:30 pm Monday - Friday County Union