Gracechurch Street is an actual location in London called Gracechurch Street. Gracechurch street is located in "City of London," which is a financial and historical site in London--I imagine this is much like an "Old Town." In Jane Austen's text, however, it is a street in London that was in a more industrial patch, which is traversed by the characters and brought up several times in the book. Contrary to my previous belief, it seems that Austen indicates that Gracechurch Street is actually an area where Mr. Darcy would be an anomalous member of the upper class: "Mr. Darcy may perhpas have heard of such a place as Gracechurch Street, but he would hardly think a month's ablution enough to cleanse him from its impurites, were he once to enter it" (Austen 151). 

Austen, Jane. Pride and Prejudice, edited by Robert P. Irvine, 2nd ed., Broadview Press, 2020.

The posted image is a photograph of Gracestreet Chuch today.