The county was named for William Tryon, colonial governor of New York.

In 1784, following the peace treaty that ended the American Revolutionary War, the name of Tryon County was changed to Montgomery County, for General Richard Montgomery, who had captured several places in Canada and died attempting to capture the city of Quebec, thus replacing the name of the hated British governor.

Its southern border abuts the northern boundary of the state of Pennsylvania.

The Susquehanna River flows southward through the eastern part of the county, enters Susquehanna County in Pennsylvania, then re-enters Broome and flows northwestward to meet the Chenango River at Binghamton.

The West Branch Delaware River flows southward along the lower portion of the county's east border, delineating that portion of the border between Broome and Delaware counties.

[7] The county's western portion is hilly, with wide valleys that accommodate Binghamton and its suburbs.

In the northern portion, Interstate 81 traverses a wide glacial valley.

The eastern part of the county is much more rugged, as the land rises to the Catskill Mountains.

The lowest point is 864 feet (263 m) above sea level, along the Susquehanna River, at the Pennsylvania state line.

16.1% were of Irish, 13.3% Italian, 12.3% German, 11.6% English, 6.4% American and 5.7% Polish ancestry according to the census.

31.00% of all households were made up of individuals, and 12.40% had someone living alone who was 65 years of age or older.

Broome has a warm-summer humid continental climate (Dfb) and the hardiness zone is mainly 5b.

Since 1964 the county has selected Democratic and Republican party candidates at approximately the same rate in national elections (as of 2024).

[34] The Broome County Law Enforcement Academy facilitates the New York State-mandated basic course for police officers, which includes over 700 hours of instruction.

All municipal police officers and deputy sheriffs within Broome County attend this academy.