U.S. House of Representatives, 1965-1998
Indiana, 9th Congressional District

The 9th district in 1964 consisted of 14 counties in southeastern Indiana: Bartholomew, Brown, Dearborn, Franklin, Jackson, Jefferson, Jennings, Lawrence, Ohio, Orange, Ripley, Scott, Switzerland, and Washington. It had 290,596 residents, 31.4% below the state district average of 417,523. With the 1965 redistricting, the first remapping in 24 years, the Democratic legislature so designed the map to give Hamilton more Democratic support, adding Clark, Decatur, and Fayette Counties, although he would have won reelection in 1966 without the additional votes. The district population was brought up to 424,933. Redistricting in 1968 added Democratic Floyd County, making him even more secure and raising his constituency to a population of 449,200. Further redistricting in 1971 added Brown and Harrison Counties plus seven townships from Monroe County (Bean Blossom, Benton, Clear Creek, Indian Creek, Polk, Salt Creek, and Washington) and two from Union County (Harmony and Union) for a total population of 472,321.

With the 1981 redistricting by a Republican legislature, Bartholomew County, where Hamilton had lived and had his main district office, was shifted to another district. Hamilton moved both home and office and was re-elected with 67% of the vote. The new 9th district included the whole counties of Brown, Clark, Dearborn, Dubois, Floyd, Franklin, Harrison, Jackson, Jefferson, Jennings, Ohio, Perry, Ripley, Scott, Switzerland, and Union plus townships in the counties of Bartholomew (townships of Jackson, Ohio, Rock Creek, Sand Creek, and Wayne), Crawford (townships of Boone, Jennings, Johnson, Ohio, Union, and Whiskey Run), Fayette (townships of Columbia, Connersville, Harrison, Jackson, Jennings, and Waterloo), Monroe (townships of Benton and Bloomington), and Washington (Brown, Franklin, Gibson, Jackson, Jefferson, Madison, Monroe, Polk, and Posey), encompassing 6,107 square miles with a total population of 544,936.

The 1990 census brought a further shift. The district now included all of the counties of Brown, Clark, Crawford, Dearborn, Dubois, Floyd, Harrison, Jackson, Jefferson, Jennings, Ohio, Perry, Ripley, Scott, Spencer, Switzerland, Union, and Washington, plus parts of Bartholomew, Fayette, Franklin, and Wayne, for a total population of 554,416. By 1995 the boundaries had been shifted to eliminate Wayne County and include all of Fayette and Franklin.

The 9th district has no central city population, the only major cities being across the Ohio River in either Kentucky or Ohio. The district's population centers have traditionally been New Albany (Floyd County) and Jeffersonville (Clark County), just across the river from Louisville, and most of the industry that existed tended to be along the river as well. Rural problems when Hamilton was elected were acute, with farmers being forced out of business, the lack of jobs leading to migration to cities outside the district, and communities facing imminent decline. The 1970 census counted 150,905 homes, of which 14,034 were without some or all plumbing. In the early 1970s only two of the district's counties met the federal guideline of one physician per 1,000 inhabitants; the 9th district average was one per 1,500 residents.

The uncertain future of large military bases scheduled for closure was a constant concern during Hamilton's career, bringing both economic and environmental challenges to the district and a need for constant oversight of the federal agencies involved.