1. Start with the geography your firm can actually serve
The U.S. Census Bureau records Ossining village as a municipality in Westchester County. Its 2020–2024 ACS five-year population estimate is 26,950, with a margin of error of 35. That is a description of the place, not evidence of legal demand, competition, search volume, leads, cases, or revenue. The practical question is narrower: does your firm want to serve Ossining, and which other Westchester County municipalities belong in the same coverage decision?
Recommended approach
Create a service-area map based on your intake policy, court coverage, travel expectations, and conflict-screening rules. Treat Ossining as one deliberate location in that map. Do not turn a population figure into a page-count target or a marketing forecast.
