Residential and commercial development have replaced many farm fields, although the county's northern part remains largely agricultural.

[2] In 2020, Hamilton County was home to three of the state's 20 largest cities and towns: Carmel (5th), Fishers (6th), and Noblesville (12th).

Geist and Morse reservoirs are two man-made lakes in Hamilton County that offer boating, fishing, and waterfront living.

In June 2008, Hamilton County was named America's Best Place to Raise a Family by Forbes.com[3] due to its strong economy, affordable living, top-ranked schools, and close proximity to Indianapolis.

[5] The land containing Hamilton County was brought into the possession of the United States by the Treaty of St. Mary's in 1818.

The application was presented to the 1822–23 session of the Indiana General Assembly, and the act was passed and approved by the governor on January 8, 1823.

However, in the 1890s, a significant number of Belgian immigrants also settled in the Noblesville area of Hamilton County.

Similarly, chain migration led to numerous first generation Serbian immigrants who had settled in Indianapolis, and their Indiana-born children, to move to Arcadia, Carmel, Sheridan, Noblesville, and Cicero around the turn of the 20th century.

[11][12] Like most of Indiana, the area was also heavily German-American, with Germans being the second largest single ethnic group in the county at the time, second only to so-called "native born whites" whose ancestry extended to the original Thirteen Colonies and who were the largest ethnic group in Hamilton County at the turn of the century.

[13] During World War I, Hamilton County was noted for an extreme rise in anti-German sentiment.

[15] During most of 1940 and 1941, Indiana as a whole was very isolationist, with much of the state preferring that the country stay neutral in the European conflict.

[19] The county is located in Indiana's 5th congressional district, which is currently (2022) represented by Republican Victoria Spartz.

Woodrow Wilson remains the only Democratic presidential candidate to carry Hamilton County, a feat he accomplished in 1912, when Theodore Roosevelt's third party candidacy split the Republican vote and allowed Wilson to carry the county with a slim plurality over incumbent President William H.

[20] Otherwise, the county has reliably voted Republican in every presidential race since 1856, prior to which it supported the Whig candidate in every election of the Second Party System.

[22] In 2024, Kamala Harris improved slightly on Biden's performance, winning 46% of the vote in the county.