Shelby County was established on February 7, 1818, and it was named for the Revolutionary War hero and the first Governor of Kentucky, Isaac Shelby. Beginning in 1820, the first county seat was located at Shelbyville. This settlement, long defunct, was located within the modern city limits of Pelham. The first courthouse was built of logs. The seat was moved to Columbia, now Columbiana, in 1826. Initially housed in an old school building, a new brick courthouse building was completed in 1854. It is now known as the Old Shelby County Courthouse and houses the Shelby County Museum and Archives. The current limestone courthouse was built from 1905–06, at a cost of $300,000.
Shelby County has a long history in agriculture, and since about 1990, it has become an important location for growing soybeans, which has exceeded cotton as the most important crop grown there.
With the advent of the automobile and the truck, Shelby County was soon crossed from north to south by U.S. Highway 31, the major one that followed the same route as the Louisville and Nashville Railroad did. (All U.S. Highways, with "one" as their last of two digits are major north-south ones: e.g. U.S. 11, 21, 31, 41, 51, 61, and 71.) The eastern part of Shelby County was later crossed by U.S. Highway 231 and U.S. 280
Decades later on, Shelby County was crossed by Interstate Highway 65. Hence, an important ingredient in the eventual growth of Shelby County has been its ready access to modern systems of transportation. Interstate 65 and U.S. Highway 31 have long provided strong connections between Shelby county and the more populous Jefferson County directly to its north, leading to suburban development in towns such as Pelham, Helena, Alabaster, and Chelsea.
According to the U.S. Census Bureau, the county has a total area of 810 square miles (2,100 km2), of which 785 square miles (2,030 km2) is land and 25 square miles (65 km2) (3.0%) is water.
Parts of Shelby County are crossed by the southernmost extensions of the Appalachian Mountains, such as Oak Mountain and Double Oak Mountain. However, large parts of Shelby County are much flatter, giving good land for farms and pastures. Shelby County also has lowlands along two rivers, and one large man-made reservoir, Lay Lake, which also borders Coosa, Talladega and Chilton counties.
Most of Shelby County is drained either by the Cahaba River, which flows along the northern edge of the county, and then to the southwest, or by the Coosa River, whose valley includes the eastern end of the county. These are both important rivers in Alabama. Much farther south, both the Cahaba River and the Coosa River flow into the Alabama River, and thence to the Gulf of Mexico. To be more precise, the Coosa River and the Tallapoosa River flow together at Wetumpka, Alabama, to form the Alabama River, and then the Cahaba River is a tributary to that one farther to the west. Waxahatchee Creek, a major tributary of the Coosa River, forms the southeastern portion of the border between Shelby County and Chilton County.
There were 54,631 households out of which 36.70% had children under the age of 18 living with them, 63.60% were married couples living together, 8.10% had a female householder with no husband present, and 25.70% were non-families. 21.70% of all households were made up of individuals and 5.20% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.04.
In the county the population was spread out with 26.30% under the age of 18, 8.20% from 18 to 24, 33.70% from 25 to 44, 23.40% from 45 to 64, and 8.50% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 96.20 males. For every 100 females age 18 and over, there were 92.60 males.
The median income for a household in the county was $55,440, and the median income for a family was $64,105. Males had a median income of $45,798 versus $31,242 for females. The per capita income for the county was $27,176. About 4.60% of families and 6.30% of the population were below the poverty line, including 7.10% of those under age 18 and 8.20% of those age 65 or over.
There were 74,072 households out of which 34.3% had children under the age of 18 living with them, 59.7% were married couples living together, 9.4% had a female householder with no husband present, and 27.5% were non-families. 23.2% of all households were made up of individuals and 6.2% had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 3.08.
In the county the population was spread out with 25.6% under the age of 18, 7.8% from 18 to 24, 29.2% from 25 to 44, 26.9% from 45 to 64, and 10.6% who were 65 years of age or older. The median age was 36.9 years. For every 100 females there were 96.0 males. For every 100 females age 18 and over, there were 95.0 males.
The median income for a household in the county was $68,380, and the median income for a family was $81,406. Males had a median income of $57,405 versus $41,692 for females. The per capita income for the county was $33,978. About 5.4% of families and 7.4% of the population were below the poverty line, including 10.3% of those under age 18 and 4.9% of those age 65 or over.
Prior to the early 1980s, elected officials serving or representing Shelby County were all affiliated with the Democratic Party. Most of the rapid transition from the Democratic Party dominance to a complete reversal, with Republicans in control of all but a couple of offices, took place during the years between 1984 and 1992. It was not, however, until the election of 2010, and specifically the results in Alabama House of Representatives District 42, that Republicans held every elected office with jurisdiction or residency (or both) in Shelby County (excludes municipal elected officials, who are elected on a non-partisan basis).
Shelby County Schools operates public schools in the county. Alabaster City Schools operates the six public schools in Alabaster. In 2014, Pelham began operating their own school system with three schools taken over from the Shelby County School System: Pelham High School, Riverchase Middle School, and Valley Elementary School.