For the past five years, I've been collecting commentary and fashion plate descriptions from the major women's journals, and have gleaned this information regarding the Season:

The Season in London officially kicked off in early January with the Queen's Birth-Day drawing room. (Although the Queen's birthday was actually in May, it was celebrated in January by custom to make it equidistant to the King's birthday in June.) The January issues of the women's magazines are always full of a listing of who wore what to the drawing room.

This roughly coincided with the opening of Parliament a couple weeks later.

The Season began drawing to a close when Parliament's session ended some time in April/May. There are several references, however, to the session's closing being delayed because of business to be concluded. London society began trickling out as the session ended.

The Season officially closed in June with the celebration of the King's Birth-Day drawing room, although this was sometime cancelled because of the King's mental illness, and discontinued entirely in 1811 when he fell ill for good. The Prince Regent revived the practice of a June drawing room circa 1816.

At the close of the season, Londoners seem to have all escaped to their country homes for a round of house parties and visits. The fashion plates for June, July and August are mostly country walking dresses, morning dresses, and informal dinner party gowns. The landowners seem to have stayed in the country long enough to oversee the harvest in late August.

The departure to the seaside and the watering places like Brighton, &c. took place in September and October. The fashion plates switch to things like "Seaside Promenade Dress" and "Brighton Walking Dress" for example. There are numerous references to the London milliners and modistes packing up their stock, closing their shops in London and moving to Bath and Brighton for these few months.

The hunting season for men did not occur until the harvest was complete and the leaves were off the trees, some time in late October and November.

By November, everyone was getting ready to head back up to London. The women's journals begin showing ball gowns, evening gowns, and Opera dress, with announcements for the upcoming theatre season, etc. The first court dress plates begin appearing in December and January.

Christmas seems to have been spent either at home in the country, or up in London, with the ladies getting ready to kick off the Season again after New Year's with the Queen's drawing room. A round of dissipatio and jollity!

Respectfully,

Louisa
Mistress of the Garderobe