The flags of the counties of the United States exhibit a wide variety of regional influences and local histories, as well as widely different styles and design principles. For example, some Floridian and Alabamian municipal flags feature a saltire, due to saltires being used on their states' flags. Some Maryland county flags feature the coat of arms of the Calvert family, as it is featured on the Maryland state flag, and due to the Calvert family's prominence in Maryland history. County flags were not always ubiquitous. Many counties went decades without a flag, until a certain event, such as a local sesquicentennial or the U.S. founding's bicentennial, spurred the creation of a flag. Frederick County, Maryland is one example, in 1976, it hosted a contest, asking the public to submit their designs to a commission. A panel then reviewed the five winning entries, choosing one to become the official county flag. Frederick County's example is typical of the flag adoption processes that many counties undertook with their flags. The 250th anniversary of Augusta County, Virginia's founding also spurred the creation of a flag, in 1988. Some flags, such as the flags of Montgomery County, Maryland, and Loudoun County, Virginia, were created by foreign entities, such as the College of Arms in the United Kingdom.
Many Floridian county flags feature their county seals on a saltire, incorporating elements from the Floridian flag, itself based on the former Spanish flag, into their designs.
Some Georgia counties are known to have no flag, including Atkinson, Baker, Banks, Barrow, and Troup Counties.
Every county in Maryland has its own flag, either officially through adoption or through custom and usage. Several Maryland county flags, such as the flags of Calvert County, Baltimore County, and Anne Arundel County, incorporate the coat of arms of the Calvert family in their designs, due to the design being featured in the Maryland state flag, and the Calvert family's prominence in Maryland history. Howard County's flag also incorporates design cues from the Maryland state flag, albeit of the Crossland banner, rather than Calvert family heraldry.
Some counties have placeholders due to Copyright issues with their seals
Some Texan county flags, such as those of Collin County, Dallas County, and McLennan County, feature design cues taken from the Texas state flag, such as the Lone Star. The Falls County flag designed by Joydelle G. Wolfram was recognized by the Texas Legislature on February 28, 1985, for optional adaptation by other counties in the runup to the state's 1986 sesquicentennial. The design has a royal blue field; on the left is a large white star surrounded by two white arcs containing 254 small stars, which represent the counties of Texas and are colored gold, red, blue, or green based on their dates of formation. On the right is the county's name, above its date of formation and a star of the correspnonding color. Counties having adopted the sesquicentennial design include Brazoria, Brazos, and Liberty (with gold star) and Denton and Hidalgo (with red star).
All 39 counties have a flag.