District of Columbia is about 397 times smaller than Ireland.

Ireland is approximately 70,273 sq km, while District of Columbia is approximately 177 sq km, making District of Columbia 0.25% the size of Ireland. Meanwhile, the population of Ireland is ~5.3 million people (4.7 million fewer people live in District of Columbia).
Tip: This to-scale comparison of Ireland vs. District of Columbia uses the Mercator projection, which distorts the size of regions near the poles.