Diamond Bar is a city located in eastern Los Angeles County, California, United States. The population estimate was 56,, up from 56, at the. Search for the person or companies you are looking for in Diamond Bar, California. For more information, please click on one of the following links: City Facts · Community Development Services · Doing Business in Diamond Bar · Economic. Find phone numbers, addresses, attractions, maps, coupons, menus, driving directions and more of great businesses in Diamond Bar, California with. Stay at the Holiday Inn hotel in Diamond Bar, California. Out hotel is a comfortable option for vacationers just outside of Anaheim and Los Angeles. Business Directory. E-mail. Print. Name: No business in this view. Diamond Bar Center | Grand Avenue, Diamond Bar , CA Phone.