Westfield is a city in Hamilton County, Indiana, United States. It is a northern suburb of Indianapolis. As of 2023, the population was 58,410. Westfield is in the Indianapolis metropolitan area.

Westfield was founded on May 6, 1834, by North Carolina Quakers Asa Bales, Ambrose Osborne, and Simon Moon. It is believed that the town was planned as a stop on the Underground Railroad with many families of the Religious Society of Friends and the Wesleyan Methodist Church supporting the cause. When the laws against aiding escaped slaves were made harsher, part of the Westfield Quaker Friends Meeting House split off into the Anti-Slavery Friends meeting.

Westfield was incorporated as a town in 1848.

On January 1, 2008, Westfield was incorporated as a city, and Andy Cook was sworn in as mayor. With recent annexations in southern Washington Township and rapid population growth in areas previously within the town limits, the city population in 2010 (30,068) was more than triple that of 2000 (9,293). Because of the growing size of the city, officials are planning a major revitalization of city's downtown. New additions to downtown Westfield are expected to include a new library and city hall.

The Union High Academy Historic District was listed on the National Register of Historic Places in 1995.

In 2014, the city opened Grand Park Sports Complex which hosted the 2016 Big Ten Conference Men's Soccer Tournament.

As of the 2020 census, Westfield had a population of 46,410. The median age was 36.4 years. 29.1% of residents were under the age of 18 and 11.7% of residents were 65 years of age or older. For every 100 females there were 96.0 males, and for every 100 females age 18 and over there were 92.0 males age 18 and over.

97.2% of residents lived in urban areas, while 2.8% lived in rural areas.