Chicago’s experience reveals the complications inherent in carrying out local gun laws around the nation. Less restrictive laws in neighboring communities and states not only make guns easy to obtain nearby, but layers of differing laws — local and state — make it difficult to police violations. And though many describe the local and state gun laws here as relatively stringent, penalties for violating them — from jail time to fines — have not proven as severe as they are in some other places, reducing the incentive to comply.

Lately, the police say they are discovering far more guns on the streets of Chicago than in the nation’s two more populous cities, Los Angeles and New York. They seized 7,400 guns here in crimes or unpermitted uses last year (compared with 3,285 in New York City), and have confiscated 574 guns just since Jan. 1 — 124 of them last week alone.

More than a quarter of the firearms seized on the streets here by the Chicago Police Department over the past five years were bought just outside city limits in Cook County suburbs, according to an analysis by the University of Chicago Crime Lab. Others came from stores around Illinois and from other states, like Indiana, less than an hour’s drive away. Since 2008, more than 1,300 of the confiscated guns, the analysis showed, were bought from just one store, Chuck’s Gun Shop in Riverdale, Ill., within a few miles of Chicago’s city limits.

Efforts to compare the strictness of gun laws and the level of violence across major American cities are fraught with contradiction and complication, not least because of varying degrees of coordination between local and state laws and differing levels of enforcement. In New York City, where homicides and shootings have decreased, the gun laws are generally seen as at least as strict as Chicago’s, and the state laws in New York and many of its neighboring states are viewed as still tougher than those in and around Illinois. Philadelphia, like cities in many states, is limited in writing gun measures that go beyond those set by Pennsylvania law. Some city officials there have chafed under what they see as relatively lax state controls.